Louis Tomlinson has jumped to his sister's defence after she revealed she was being hounded by an online stalker.

The One Direction hunk, 21, was left fuming after his sibling Lottie, 15, told him, just before his band performed at the Etihad Stadium in Manchester last week, that she was being chatted up by a 24-year-old man on Twitter.

The angry singer reportedly immediately phoned the man, who had also allegedly been sending Lottie racy text messages and semi-naked photographs of himself, and warned him to stay away from his sister.

A source told the Daily Star newspaper: ''Louis wanted to be focused on playing at one of the biggest venues in the country but his sister comes first and he wanted to make sure he was protecting her.

''He didn't hold back when he called the bloke. He was really angry about what had been going on.''

It is believed Louis had met the man in the past after he pretended to be friends with the popular boyband - consisting also of Harry Styles, Zayn Malik, Niall Horan and Liam Payne - in order to get close to Lottie.

Lottie has since deactivated her account on Twitter, telling her followers that she was leaving the social networking site for a while.

She tweeted: ''Coming off Twitter for a bit, bye.''