Taylor Swift's 'I Knew You Were Trouble' is ''100 per cent'' about her on/off romance with Harry Styles, which played out over 2012.
The US singer had an on/off relationship with the One Direction hunk last year, with them initially splitting in April when he was spotted kissing a model in Australia.
They then reconciled for two months at the end of the 2012, but split over New Year while holidaying in the British Virgin Islands. Now a friend has confirmed Taylor's single 'I Knew You Were Trouble' - one of her famous break up songs about her exes - is about their romance.
The source told RadarOnline.com: ''Taylor was crushed over Harry the first time they dated, and like she always does, she penned a song about him to deal with her broken heart.
'' 'I Knew You Were Trouble' is one hundred percent about Harry. She knew he was young and popular with the ladies and wasn't ready for a serious relationship, but somehow hoped she could make it work.''
The lyrics to 'I Knew You Were Trouble' feature the lines: ''I knew you were trouble when you walked in / So shame on me now / Flew me to places I'd never been / Until you put me down.''
In another part of the song, Taylor sings: ''When your saddest fear comes creeping in / That you never loved me / or her or anyone or anything.''
The source added Taylor was thrilled when she got back together with the pop hunk in October, adding: ''She was head over heels for Harry so even though she knew he was bad news for her, she gave him another chance.''
Taylor is currently preparing to go on tour. Meanwhile Harry - who has remained single since his split from Taylor - was last night (18.02.13) spotted at the O2 and War Child BRIT Awards Concert with Muse at O2 Shepherds Bush Empire in London, where he was chatted with another of his ex-girlfriends, model Cara Delevingne, as well as flirting with Cara's best friend, singer Rita Ora, in the VIP bar.