Rihanna and Chris Brown collaborate on new remixes

Rihanna and ex-boyfriend Chris Brown are back together musically after appearing on each other's remixes.

Brown is on a remix of Rihanna's Birthday Cake while she's on a version of his track Turn up the Music.

The songs appeared on the internet on Monday, with both stars tweeting links to the tracks.

Rihanna was attacked by Brown in 2009 and the R&B singer later pleaded guilty to the charge. He's still serving five years' probation for the attack.

Relations between the pair seem to have improved though, and last year Rihanna didn't object to the lifting of a restraining order on Brown.

The remixes of their current singles appeared - ironically enough - on Rihanna's birthday.

The Barbadian singer turned 24 yesterday and is performing at tonight's Brit Awards alongside the likes of Adele and Coldplay.

Rihanna and Chris Brown first collaborated in 2007, on a remix of the star's breakthrough hit Umbrella.