Harry Styles was the only member of One Direction to not attend his ex-girlfriend Taylor Swift's Billboard Music Awards after-party.

The 21-year-old 'Best Song Ever' star flew back from Las Vegas - where the awards were held on Sunday night (17.05.15) - to Los Angeles on his own, in order to avoid seeing the 25-year-old singer and her new boyfriend Calvin Harris getting cosy at Taylor's celebrations at the Caesar's Palace hotel.

Harry dated Taylor for four months, before the couple split in 2013.

A source at the Billboard Music Awards - where Harry, Louis Tomlinson, Niall Horan and Liam Payne won two awards between them - said: ''(Harry) realised the party wasn't a good idea, so flew back to LA solo.''

Speaking to The Sun newspaper, a 1D spokesman added: ''Harry didn't stay in Vegas after the awards, so didn't attend any after-show party.''

While Taylor was celebrating winning eight Billboard awards, Calvin's ex-girlfriend Rita Ora stayed backstage throughout the event - held in MGM Grand's Garden Arena - in order to avoid the 31-year-old DJ making out with Taylor in front of the biggest names in the music industry.

An insider at the event said: ''Rita was backstage the whole night to avoid Calvin and Taylor. The romance is big news -- she wanted to avoid an awkward encounter or being pictured reacting. Taylor was introducing all her mates to Calvin by his real name Adam, telling everyone how happy they were.

''There's no love lost between them.''