Michelle Williams on the cover of Vogue. (Annie Leibovitz/Vogue)

The actress plays the doomed starlet in “My Week With Marilyn,” a film about the making of the 1957 movie “The Prince and the Showgirl.” It’s scheduled to open this November.

The very thin actress told interviewer Adam Green she was unable to gain the weight to play Monroe — in the right places.

“Unfortunately, it went right to my face,” she said. “So at some point it became a question of, ‘Do I want my face to look like Marilyn Monroe’s or my hips?’ ” Williams was ultimately given a figure boost with foam padding.

The two time Oscar nominee also talked about her ex-partner Heath Ledger, who died of an accidental overdose in 2008. The couple have a 6-year-old daughter.

Williams told Vogue his death “changed how I see the world and how I interact on a daily basis.

“It’s changed the parent I am. It’s changed the friend I am. It’s changed the kind of work that I really want to do. It’s become the lens through which I see life — that it’s all impermanent.”

As for their child, Matilda, Williams hates seeing her privacy invaded by fans and paparazzi. “I’m going to do everything in my power to make her feel safe and protected, and to extend her childhood for as long as possible,” she said.

Check out more photos of Williams as Monroe here. Click through to see a larger view of the cover.