Johnny Whitaker, Plato's former manager and a friend of the family, told ABCNews.com he once tried to intervene in Lambert's drug use.
"I did say, 'You know your mother had a problem, which means you may have a problem because it is a family disease,'" said Whitaker, a former child actor who played Jody on "Family Affair" and is now a certified drug counselor. "Dana passed away because of the disease. And when the toxicology reports come in, I'm sure they will show something."
Lambert, 25, committed suicide on May 6, just days before Mother's Day and the 11th anniversary of Plato's 1999 death from a drug overdose.
In the days leading up to Lambert's suicide, a long-time family friend told Whitaker that Lambert had "become very withdrawn and hadn't talked to anybody for three or four days." The same friend told Whitaker that Lambert always said, "he wanted to be with Mom."
The Tulsa, Okla., office of the Chief Medical Examiner confirmed to ABCNews.com that Lambert died last week from a self-inflicted shotgun wound to the head. Toxicology test results are still pending.
Whitaker said Lambert's family once asked him to talk to the young man, an aspiring rapper and singer, about his drug use. At the time Lambert only admitted to using marijuana, Whitaker said.
"I kept the door open and let him know I would be there," Whitaker said. "He wasn't ready to work on it."
Lambert was just 14 when his mother took her own life, overdosing on prescription pills on May 8, 1999. She was 34 when she died.
Plato married Lambert's father, Lanny Lambert. in 1984. Tyler was born a year later. The couple divorced in 1990, and Lanny Lambert was given custody of Tyler.
Even though Lambert mostly grew up with his paternal grandmother, Joni Richardson, he was attached to his mother.
"Dana did absolutely adore her son," Whitaker said.
But he also said Lambert thought he had a closer relatonship with his mother than he really did.
"They didn't," Whitaker said. "Emotionally they did. Physically and actually, they didn't."
Nonetheless, Lambert struggled every Mother's Day.
"Mother's Day was always a difficult time, not only because it was Mother's Day but the anniversary of Dana's death," Whitaker said.
Dana Plato's Difficult Life
Plato appeared to have a bright future ahead of her when she landed the role of Kimberly Drummond on "Diff'rent Strokes." The show was a hit from its 1978 premiere, and Plato charmed audiences. But she was written off the series in 1984 amid rumors of drug use, and she struggled to find other roles.
In 1989, Plato bared all for Playboy and began starring in B-movies. From there, she dabbled in softcore pornography, including a 1997 feature based on her "Diff'rent Strokes" past.
Meanwhile, legal and substance abuse problems plagued the actress. In 1991 she was arrested attempting to rob a video store at gunpoint, and the following year she was arrested for forging a Valium prescription.
Plato's drug addiction eventually took her life -- she died after overdosing on Vanadom and Vicodin.
Troubled Stars of the 1980s
Here are the stories of nine other child stars from 1980s TV who ended up plagued with problems.
In February, family and friends found "Growing Pains" actor Andrew Koenig's body in a Vancouver, British Columbia park, after he went missing for nearly two weeks.
His father Walter Koenig, an actor best known for his role as Chekov on "Star Trek," said his son killed himself after a liftetime suffering from depression.
Though the 80s made him a star, Koenig had been trying to escape his fame as "Growing Pains" goofball Richard "Boner" Stabone.
At the time of his disappearance, his father told ABC News: "He's been depressed. He's trying to get ahead in this business, and he's been working at it a long time."
The younger Koenig, who appeared on "Star Trek: Deep Space Nine" and played The Joker in 2003's "Batman: Dead End," hated being known for his "Growing Pains" role and "Star Trek" connection, according to his friend, writer/producer Lance Miccio.
"When I introduced him to people, he said, 'Never say my dad's Chekov and never say I played Boner,'" Miccio told ABCNews.com. "He didn't want to be known as Boner his whole life. That's something that affected him."
Koenig's "Growing Pains" co-star, Tracey Gold, has also whethered the ups and downs of Hollywood. Gold rocketed to teen stardom after being cast as Carol Seaver in the series.
But while she thrived on TV, behind the scenes, Gold struggled with anorexia. In 1992, her mother, Bonnie Gold, told People magazine that she burst into tears when she visited her daughter on the "Growing Pains" set in 1985 and was shocked to find she had wasted away to 90 lbs.
After seeking treatment in the early '90s, Gold transitioned from "Growing Pains" to acting in TV movies. But in 2004, she was arrested for driving under the influence after she rolled her SUV, carrying her husband and her three young sons, down a California highway embankment.
Gold's 7-year-old son, Sage, sustained the worst injuries, a broken clavicle and a head wound. The actress spent five hours in prison before being released on $50,000 bail. Gold later plead guilty to a felony DUI charge and was sentenced to one month in a work release program, 240 hours of community service, and three years of probation.
In September 2009, actress Mackenzie Phillips revealed to Oprah Winfrey that her rock star father, John Phillips, raped her at age 18, sparking a 10-year-long consensual sexual relationship. Phillips, 49, the former star of '70s-'80s sitcom "One Day at a Time," said she was first raped by her father, the lead singer of the Mamas and the Papas, in a hotel room while passed out after a drug binge. (She also has a history of substance abuse issues.)
The relationship continued long after she married Jeff Sessler when she was 19-years-old, and ended only when she became pregnant and feared her father was the baby's father, Phillips said. Her father paid for an abortion. "I woke up that night from a blackout to find myself having sex with my father," Phillips said on "Oprah," reading an excerpt from her new book, "High on Arrival." "I don't know how it started."
During the 1980s, television was Corey Feldman's oyster. After landing a starring role in a McDonald's commercial at age three, he appeared in dozens of television shows, including "Mork and Mindy," "One Day at a Time," "Cheers" and "Eight is Enough." Feldman successfully crossed over into film, co-starring in box office boons like '85's "The Goonies" and '86's "Stand By Me."
But Feldman's success couldn't solve his problems. He worked constantly to escape parents who he claimed abused him, and at age 15, was granted legal emancipation from Sheila and Robert Feldman. Neverending exposure to the Hollywood lifestyle led to an appetite for drugs, and in 1990, Feldman was arrested for heroin possession -- twice. He went to rehab the following year.
"It took people a long, long time to forgive me. I was just a kid making mistakes like any other kid," he told the Phoenix New Times in 2000.
These days, Feldman's back on his feet. In 2002, he channeled his trials and tribulations in the business into a solo album, "Former Child Actor" and appeared on the first season of VH1's "The Surreal Life." He currently stars in the A&E reality TV series "The Two Coreys" with fellow '80s child star, Corey Haim.
"Full House" sweetheart Jodie Sweetin didn't grow up to resemble her goody-two-shoes character at all. At age 22, the star of the '80s and '90s sitcom developed a debilitating daily meth habit that she kept a secret from her then-husband, LAPD officer Shaun Holguin.
In 2005, after a night of partying landed her in the hospital, Sweetin sought treatment. Once sober, she divorced Holguin and married Cody Herpin, the father of her daughter Zoie.
But in November 2008, Sweetin split with Herpin. Last year, she came out with the book "unSweetined," in which she reveals she kept the meth, cocaine and ecstasy binges going while she claimed to be sober. In one passage, she talks about breaking into tears while addressing a crowd at Wisconsin's Marquette University about her "trials and tribulations."
"I talked about growing up on television and about how great my life was now that I was sober, and then midspeech I started to cry," Sweetin writes. "The crowd probably thought that the memories of hitting rock bottom were too much for me to handle. Or maybe they thought the tears were just a way for an actor to send a message that drugs are bad. I don't know what they thought."
"I know what they didn't think," she continues. "They didn't think I was coming down from a two-day bender of coke, meth, and ecstasy and they didn't think that I was lying to them with every sentence that came out of my mouth."
Who would've expected Screech to turn into a sexual freak? Dustin Diamond, who played the loveable nerd Samuel "Screech" Powers on "Saved by the Bell" and its precursor, "Good Morning Miss Bliss," through the late '80s and '90s, seemed allergic to scandal as a teen.
But in 2006, Diamond released a sex tape, "Screeched," aka "Saved By the Smell." It depicted the TV nerd in more detail than any fan wanted to see, and Diamond was panned for participating in the decidedly un-sexy endeavor.
His manager, Roger Paul, told the New York Daily News that he hoped the tape would raise Diamond's profile and help him get back into acting of the non-pornographic variety. Still, Diamond's relying on his past to get him through the present. Last year, he released "Behind the Bell," a book about his sitcom days in which he claims that drugs and sex were the rule on the "Saved by the Bell" set.
Plato's "Diff'rent Strokes" co-star, Gary Coleman, has seen his fair share of troubles. While he turned into a pop culture icon thanks to his signature line on the show, "What'choo talkin' 'bout, Willis?," Coleman became infamous for his problems with the law.
In 1989, Coleman sued his parents and former manager over misappropriation of his $3.8 million trust fund.Though he won a ruling in excess of $1.2 million in 1993, Coleman filed for bankruptcy six years later, and blamed his financial problems on mismanagement of his trust.
Coleman has also been cited for disorderly conduct multiple times, and in 1998, was charged with assault after punching bus driver Tracy Fields. He plead no contest and was ordered to pay Fields' hospital fees. Most recently, in January, he was arrested on a domestic violence assault warrant in Utah, and spent a night in jail.
Adam Rich may have charmed audiences as adorable Nicholas Bradford on "Eight Is Enough," but in real life, his shenanigans have been far from cute.
After leaving "Eight Is Enough" in 1981, Rich made a handful of guest appearances on shows including "CHiPS" and "Baywatch." Apparently, those guest roles didn't give him enough dough. In 1991, he was arrested for breaking through a pharmacy window in an attempt to steal drugs. He was bailed out of jail by his "Eight is Enough" dad, Dick Van Patten, only to be arrested for shoplifting again.
Rich pleaded no contest to both charges, but his legal troubles didn't end there. In 2003, he racked up a misdemeanor DUI arrest after almost smashing into a police car in Los Angeles, and also plead no contest to those charges.
Jamiee Foxworth's post-'80s TV career is one her "Family Matters" dad would probably condemn.
After playing youngest daughter Judy Winslow on the sitcom from 1989 to 1993, Foxworth was written out of the show with no explanation. The actress turned to drugs and alcohol and attempted to supplement her meager funds by starring in pornographic movies under the name Crave.
In 2008, Foxworth sought help for her substance abuse problems by participating in VH1's "Celebrity Rehab With Dr. Drew." She gave birth to a baby boy in May 2009 and told People magazine, "I've been through a lot of pain in the past and … I now look forward to years of joy to share with my child."