Philipps, 39, who is godmother to the pair’s daughter Matilda, writes in her book that she had a feeling her friends would one day reunite.
“He and Michelle were in the process of separating at that point, and I felt sad for both of them but weirdly like something would be figured out and it wasn’t the end of the story for them,” Philipps writes.
“They were so young and that baby was the light of both of their lives,” she continues. “They were just working all the time and it was complicated.”
“S— is always complicated. Especially when you’re twenty-eight. And movies stars. With a baby,” Philipps adds.
Ledger and Williams dated for three years after meeting on the set of their 2005 film Brokeback Mountain. The two split in 2007.
RELATED VIDEO: Michelle Williams Secretly Marries Indie Musician Phil Elverum
While the two never rekindled their relationship, Williams keeps his memory alive by talking about him to their daughter, now 12.
“I always say to Matilda, ‘Your dad loved me before anybody thought I was talented, or pretty, or had nice clothes,” Williams told Vanity Fair in a recent interview.
Williams also revealed she had secretly married musician Phil Elverum this summer.
This Will Only Hurt a Little is available now for purchase.