Taylor Swift Harry Styles Liam Horan
Harry Styles, Taylor Swift and Liam HoranGetty

When it comes to dating your friend's ex, most of us know that's a no-no.

But it seems One Direction star Niall Horan is not bothered one bit.

The Mirror claims the 20-year-old singer has been cosying up to Taylor Swift, former girlfriend of his bandmate Harry Styles.

The Irish lad recently paid the country songbird a special visit at London's O2 arena during the UK leg of her music tour.

A source told the paper: "Taylor was happy to sort Niall some access all areas passes and even had drinks with him before the show."

Styles dated Swift at the end of 2012 but their whirlwind romance quickly fizzled out and he broke up with the I Knew You Were Trouble songstress in January 2013, while on holiday in the Caribbean.

Horan, who has been spending time catching up with his music interests while he recovers from a knee operation, may have crossed a friendship line by spending quality time with Swift following her acrimonious split from Styles.

"They met through mutual friend Ed Sheeran. Niall seemed like a genuine fan of Taylor's music. However, he smirked when she performed I Knew You Were Trouble, which was rumoured to be about Harry."

Swift and Horan's O2 encounter comes amid reports that the One Direction star and his model girlfriend, Barbara Palvin, are on the rocks.

The lovebirds are said to have taken a break from their romance after the beauty relocated to Paris to boost her career.

Meanwhile Styles, who has also been romantically linked to British model Cara Delevingne, Rod Stewart's daughter Kimberly and model Daisy Lowe in recent months, is said to be dating Keeping up with the Kardashians star Kendall Jenner.