The death of Heath Ledger transformed his friend Jake Gyllenhaal's outlook on life.
The two actors became close while filming 2005 movie Brokeback Mountain, and Jake admits his co-star and friend's accidental drug overdose in 2008 has affected him so deeply that he struggles to talk about it publicly.
"Personally, it affected me in ways I can't necessarily put in words or even would want to talk about publicly," the 35-year-old tells Entertainment Weekly. "In terms of professionally, I think I was at an age where mortality was not always clear to me."
Jake admits Heath's death made him rethink his success story in Hollywood, confessing the experience of working with someone who died young left him struggling to care about box office records.
"I think you live in this bubble of making films... there are real friends, and there is a real community," he says. "I think it (gave me) the experience of, 'This is fleeting'. And none of the attention or synthesized love that comes from the success of a film really matters at all.
"What matters is the relationships you make when you make a film, and the people you learn from when you're preparing for a film. That changed a lot for me."
Jake has previously spoken movingly about his late friend's work on Brokeback Mountain, which focused on the gay relationship between two cowboys.
"It was an intimate and really scary thing for me and Heath, in particular, to dive into," he told America's National Public Radio last year. "It was uncomfortable for both of us in some of the scenes, and yet we both deeply believed in what the movie was saying."