Singer Janet Jackson and the rest of the Jackson clan were unaware that Michael Jackson was using propofol, a powerful sedative typically used in operating rooms, she told ABC News' Robin Roberts in an exclusive interview.
"That was, that was a shocker to me and it just -- that's serious," Jackson said. "That's heavy. That's heavy. None of us knew to that extent."
Toxicology results showed that Michael Jackson had lethal amounts of propofol in his system when he died, along with a cocktail of other prescription drugs. His death was ruled a homicide.
But the family was not naive about her brother's drug problem, Jackson said, adding that she reached out to him throughout the years but was unsuccessful.
"I did," she said. "Of course, that's what you do. Those are the things that you do when you love someone. You can't just let them continue on that way. And we did a few times. We weren't very successful."
Jackson said her brother understood that the family's motives for the interventions were out of love.
"How do I say this? Understanding. I guess that will be the best way to -- understood that it was out of love, because of caring. But when it's something like that, people can tend to be in denial," she said.
When asked if her brother was in denial about his addiction, she replied, "Possibly."
"I wish he could answer this question for you and not me," she said. "I felt that he was in denial."
The five-time Grammy award-winning artist said that she was "incredibly close" to older brother Michael; but the siblings went through long stretches without seeing one another, and Michael slowly succumbed to a dangerous spiral of drugs and addiction.
"You can't make 'em drink the water. ... I'm a true believer in prayer, a big believer in prayer -- but it's, it's something that you can't do for them. Something they have to do for themselves," she said.
Michael Jackson's personal physician, Dr. Conrad Murray, has admitted to administering propofol but has denied giving Michael anything that should have killed him.
Murray is still under investigation in Los Angeles. The district attorney's office has yet to announce any charges against him in Jackson's death, but on Monday, Murray appeared in court on charges that he owes more than $14,000 in child support.
Murray agreed to start making payments to avoid jail time but claimed he had to close his practice because of threats he received after Jackson died.
Janet Jackson said she wants to see that Murray is never allowed to practice medicine again.
"He was the one that was administering," told Roberts. "I think he is responsible."
For Jackson, her interventions with Michael through the years echoed the trials of her first marriage to James DeBarge, who has admitted to being addicted to prescription medication.
"It kinda goes back to my first relationship, something that you have to want. ... it's something they have to want," she said of her desire to rid both Michael and DeBarge of their addictions.
At 18, Jackson's marriage to DeBarge, part of a family singing sensation billed as the next Jackson 5, was an act of rebellion. The two eloped without the approval of her parents.
"I wanted to be on my own and get out of the house," she said. "We were the kind of kids that -- we -- obeyed our parents, really obeyed our parents. If they said no, you don't ask why. You just understand that it's no."
But DeBarge's struggle with addiction broke the marriage in less than three months.
"He was my first love and very much so," she said. "And there was a lot going on in our relationship, a lot going on with him, I should say. And -- just being so young and not really -- not really knowing what life is really all about, just beginning to explore life and wanting to -- help him, thinking I could change him, if I only could do this and that, and not realizing that it was something that he had to do and want for himself."
Their marriage was annulled and she did not find love again until she met Rene Elizondo Jr., a songwriter and one of her musical collaborators. The two were secretly married for eight years, but it ended with a painful divorce.
Music producer and record company executive Jermaine Dupri was the latest man in Jackson's life. The couple dated on and off for seven years, producing two of her chart-topping albums together, but parted ways. Their relationship made headlines this summer when rumors of a possible marriage circulated.
For the pop star who has gone to great lengths to keep her private life hidden, Jackson addressed the rumors, telling Roberts that she was not married to Dupri.
"No, I'm not," she said. "I know people thought we were. … I just heard that today. Someone said to me, or just yesterday, someone said, 'You engaged,' and I said, 'Who am I engaged to?' And they said to Jermaine. I said, 'Oh, I am?'"
In fact, she confirmed that they are no longer together.
"I adore him. Absolutely adore Jermaine," she said. "Love him to death and we're still very good friends to this day. Very good friends, but that's all I'll say."
Jackson said she is single and focusing on her work -- a new music video for her single, "Make Me," and a book entitled "True You," a personal story about her lifelong struggle to control her weight.
Between 100 million records sold, five Grammys and legions of fans around the world, it's hard to believe that Jackson has spent a lifetime in search of her true self.
"Just picking yourself apart all the time because you're so used to being kind of picked apart," she said. "'Oh, your butt's too big,' and 'you've got too much meat here,' 'got too much this there.' ...Well, now I know there's nothing wrong with [my booty], thank you to Jermaine Dupri."
Five months since Michael's death, Jackson said she has found refuge in her work.
"I needed to get back to work. It helped me get through it," she said. "I was able to put a lot of my focus someplace else."
With the release of the documentary "This Is It," which shows Michael preparing for his sold-out summer concert tour, she has been bombarded by painful images of Michael.
"I haven't seen [the film]. I definitely won't, not right now. I don't know if I will ever see it," she said. "...It's hard when I see a poster, you know, the "This Is It" posters that are around the city. That's tough. I've seen the commercial. They advertise -- the trailers -- on TV. That was tough."
If her brother were here, she told Roberts he would tell her to "stop and enjoy" life.
"I think it would be to stop and enjoy. I think that would be it," she said.
It's advice she may well heed during this time of shifting priorities and self-reflection.
"I'm in a different space. There's a lot that's gone on, a lot that makes you think, think about life. Something that I think we tend to -- at times take for granted," she said. "I'd love to have a family."
Jackson recently released a CD called "Number Ones." She recorded the CD's only new single "Make Me" after Michael's death. "It's classic -- classic me," she said. "Dance, upbeat, lots of harmonies."
At 43, the princess of pop tells Roberts she's finally come to embrace herself.
"[Forties are] great. You know why? You don't care what people think. You really don't. ... You do your thing," she said. "You have no time for mess, no time for drama."
Watch Robin Roberts' exclusive interview with Janet Jackson, "In the Spotlight," Wednesday, Nov. 18 at 10 p.m. ET.