Justin Bieber has written a song about claims he fathered child.

The Baby singer is in London to launch his new album Believe.

And, at a playback of the album at Supperclub, he revealed that the drama he went through has inspired a song.

He told the Metro: "That girl who said she was gonna have my baby, Mariah Yeater, there's a song about her."

Justin denied claims he had fathered Yeater's son and offered to have a DNA test, but she eventually dropped the paternity case.

At the playback of the album, the teen star also unveiled a song he wrote for his fans on his 18th birthday.

According to the Daily Mirror, Justin revealed he spent the evening of his 18th birthday writing a song - also called Believe - to thank the Beliebers for their support.

"This is a song I wrote for my fans and it's about how they inspired me," Justin said.

"It means a lot to me as I wrote it at 12pm on my birthday," he added.

The album, which isn't out until June, was praised by the newspaper's reviewer Natalie Edwards, who wrote: "It's a strong comeback from the Baby singer which shows his progression both personally and professionally."