The 33-year-old singer started a spat with the former Girls Aloud member over 10 years ago, after she recorded a song in which she claimed she wanted to look like Cheryl, before saying ''nobody really wants to look like'' the singer.
And Lily has now issued an apology to the 'Fight For This Love' hitmaker - who has 18-month-old son Bear with her former partner Liam Payne - as she blamed her harsh words on being ''angry'' about the fact she'd ''never even had an orgasm''.
In an excerpt of her upcoming book 'My Thoughts Exactly' which was obtained by The Sun on Sunday, the 'Trigger Bang' singer wrote: ''I was frustrated. I was struggling with my own issues around sexuality. I'd never even had an orgasm. And then here were these gorgeous girls - my peers, my colleagues so to speak, and co-workers - taking their clothes off with wild abandon and being loved and rewarded for it. I couldn't take it.
''Sorry Cheryl. I was angry because I hadn't come yet. It was ridiculous. I b****ed at Cheryl because she insulted me after I provoked her. You can see how to can go, this play-ground game. The crazy part was as if the hatred was a real thing. We didn't know each other. I'd never met Cheryl. I did resent Girls Aloud's success back then, though.''
After releasing the track - fittingly titled 'Cheryl Tweedy' - in 2006, Lily then took to her blog to slam the brunette beauty.
The 'Not Fair' hitmaker - who has daughters Ethel, six, and Marnie, five, with her former husband Sam Cooper - wrote: ''Cheryl, I don't really want to look like you. I was being ironic. Nobody really wants to look like you, they just think they do.''
Cheryl, 35, later hit back at Lily, calling her a ''chick with a d**k''.