According to FemaleFirst, the 27 year-old actress, who plays a character inspired by Edie Sedgwick in the film I’m Not There, did not attend a party at the Bowery Hotel in New York on Tuesday.
A source said, "Michelle was notably absent from the party but Heath was there enjoying himself. Although he was looking a little dishevelled and very scruffy."
Ledger was joined at the party by his co-stars, Richard Gere and Julianne Moore.
Michelle Williams and Heath Ledger, who are the parents of a two year-old daughter, announced their separation last September.