Ledger, star of "Brokeback Mountain" and "The Dark Knight," died of an accidental drug overdose in 2007.
He and Williams were no longer dating at the time of his death; however, they have a young daughter and continued raising her together despite the split. Since his death, Williams has said little in public about losing him.
"In a strange way, I miss that year, because all those possibilities that existed then are gone," UsMagazine.com quoted Williams as saying about the year after Ledger's death in an interview for TV's "Nightline."
"It didn't seem unlikely to me that he could walk through a door or could appear behind a bush," Williams explained. "It was a year of very magical thinking, and in some ways I'm sad to be moving further and further away from it. ... I've found meanings around the circumstance, but the actual event itself still doesn't... I can't find a meaning for it. I can find meanings in things and people and relationships that have sprung up, and friendships that have strengthened. I can find a lot of meaning in that, but not in why. I know I got kind of obsessed with that for awhile, the before and after. A lot of things died... There's a line from a book that gave me so much comfort and it said, 'When you've truly lost everything, then at least you can become rich in loss.'"