Lily Collins has written an emotional open letter to her singer father Phil, forgiving him for "not being the dad I expected".

The 27-year-old actress is one of former Genesis star Phil's five children, by three different wives. Lily has penned a debut book entitled Unfiltered: No Shame, No Regrets, Just Me, in which she tackles her sometimes difficult relationship with her father, who was frequently absent as she was growing up.

In an open letter published in the book, Lily writes: "I forgive you for not always being there when I needed and for not being the dad I expected... I forgive the mistakes you made. And although it may seem like it’s too late, it’s not. There’s still so much time to move forward."

Lily is the only child from Phil's marriage to antiques dealer Jill Tavelman. Phil and Jill split in 1994, at which time Lily and her mother moved to Los Angeles, with the Rules Don't Apply star only seeing her father during the school holidays.

Lily continued her letter, which forms part of a collection of essays aimed at teenage girls, by writing of Phil: "We all make choices and, although I don’t excuse some of yours, at the end of the day we can’t rewrite the past.

"I’m learning how to accept your actions and vocalise how they made me feel. I accept and honor the sadness and anger I felt toward the things you did or didn’t do, did or didn’t give me."

In Lily's book, she also opens up about her battles with eating disorders anorexia and bulimia, which she says were partly caused by the stress of her father's divorce from Orianne Cevey, his third wife, in 2008.

Recalling the difficult period, Lily wrote; "Not only did I start viewing myself differently physically, but I began limiting my happiness by controlling my eating habits.

"I couldn’t handle the pain and confusion surrounding my dad’s divorce, and I was having a hard time balancing being a teenager with pursuing two different grown-up careers."

While Lily and Phil are now moving on with their relationship, the actress admits a "terrible disconnect" grew between her and her father as she grew up, adding: "Many of my deepest insecurities stem from these issues with my dad."

Last year (16), Phil revealed he had reunited with Orianne and they were living together in Miami, Florida.