Michelle Williams and daughter Matilda Check out the trailer for "Blue Valentine" below as well as Michelle Williams' interview on "Nightline".

The “Blue Valentine” star says she is still trying to make sense of the death of her former partner, Heath Ledger. The actress, who was sharing parenting duties of their daughter Matilda, told “Nightline” a normal upbringing for her toddler “is of more importance to me than anything else.

Michelle Williams says she is "sad to be moving further and further away" from the death of Heath Ledger, her ex-boyfriend and father of 5-year-old daughter Matilda.

The 30-year-old actress made her comments on
 ABC's "Nightline" television news program in an interview to promote her new film "Blue Valentine". She and Ledger starred together in the 2005 movie "Brokeback Mountain", which earned her an Oscar
nomination. Williams said they fell in love on the set.

"Maybe that's the secret," she said of their romance. "That was happy at work."

Ledger was found dead in his New York apartment in 2008, months after he and Williams broke up after a three-year relationship and after he filmed his chilling role as the Joker in the Batman film "The Dark Knight". He died of an accidental overdose of prescription medication.

"It didn't seem unlikely to me that he could walk through a door or could appear from behind a bush," Williams said. "It was a year of very magical thinking and in some ways I'm just sad to be moving further and further away from it. I found meanings around the circumstance, but the actual event & I still can't find it."

In "Blue Valentine", Williams and Ryan Gosling play a married couple whose lives from various time periods are shown throughout the movie. The film was initially given an NC-17 rating and was reduced to an R earlier this month, which would allow it to be screened in more theaters. It is set for release at the end of December.

Williams and Gosling have denied recent reports that suggest the two have become romantically involved.

"Creatively, we are doing it," Gosling joked to "Nightline". "No, we're professionals."

Williams also recently filmed the movie "My Week With Marilyn", playing Hollywood icon and sex symbol Marilyn Monroe. The film depicts the late actress' 1956 film shoot of the movie "The Prince and the Showgirl" in London opposite Sir Laurence Olivier, who is portrayed by Kenneth Branagh and is due to hit theaters in 2011.