Cory Monteith and Lea Michele: Their Love Through the Years
PHOTO: Cory Monteith and Lea Michele attend the 12th annual Chrysalis Butterfly Ball on June 8, 2013 in Los Angeles.

When Cory Monteith and Lea Michele began working together on "Glee" in 2009, they insisted that their relationship was purely platonic. However, after a few years (and a break-up for Michele), things changed, and the two fell in love. "I don't even remember a time when he wasn't my boyfriend," the actress, 26, told Marie Claire in its January 2013 issue. "No one knows me better than Cory."

Beginning as Friends, 2009

"Glee," a TV show about a high school glee club, premiered on FOX in 2009 and its close-knit cast, including Monteith and Michele, stayed close in the wake of instant fame. "Cory is such a goofball," Michele told Glamour in 2010. "I swear to God, that kid can make me laugh!"

Could It Be Love? Early 2010

As their on-screen relationship heated up, so did rumors that Michele and Monteith were dating. However, Michele, who was at that point dating actor Theo Stockman, shot them down. "No, I don't have a crush on Cory!" she told Glamour magazine that summer. "He's like my brother."

Michele Back on the Market, 2011

Michele split with her boyfriend of one year, Stockman in the fall of 2011. Naturally, rumors of an off-screen romance between the actress and Monteith (at a "Glee" taping that October) intensified.

It's Official! 2012

Just a few months after Michele's break-up, she and Monteith (at the People's Choice Awards in January) made their debut as a couple. In May, Michele tweeted, "I'd like to be the first to wish a very special bday to a very special person @CoryMonteith.. happy birthday:) <3 Let the festivities begin! Lots to celebrate today:)" and afterward, the two were photographed cuddling outside of an L.A.-area deli and kissing at a hockey game in New York City.

One of Hollywood's Most Celebrated Couples, early 2013

The "Glee" stars kicked off 2013 with a romantic trip to Hawaii, and the next month, looked very much the solid couple at an event honoring "Glee" creator Ryan Murphy in Beverly Hills. "For the first time in my life, I feel really, really settled and happy," Michele told Marie Claire. "I feel like the luckiest girl in the world."

Standing By Her Man, March 2013

Days after the two attended a hockey game together in L.A., Monteith's rep confirmed to ABC News that the actor "voluntarily admitted himself to a treatment facility for substance addiction." His girlfriend stood by him. "I love and support Cory," she said in a statement. "I am grateful and proud he made this decision."

Coping with Loss, July 2013

In the wake of Monteith's death, Michele (with Monteith last month) is struggling to cope with the loss of her partner. "We ask that everyone kindly respect Lea's privacy during this devastating time," her rep told ABC News in a statement.

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