Heath Ledger and Michelle Williams

Ledger and Williams, who met on the set of Brokeback Mountain, have been engaged since 2004 and have a 23-month-old daughter, Matilda.

But friends say their busy schedules mean they are rarely together and People.com is reporting that they've now decided to split.

A source tells the website, "It was rocky for a while. They did what they could to make it work."

Source: WENN