The Barbados-born singer – who made a return to the UK this week to preview her uop LP 'Rated R' and it's dark new sound – wanted it to be even rockier but her record label had a 'seizure'.

The 21-year-old star approached guitarist Nuno Bettencourt, of US band Extreme, to play on the record but Rihanna's record label stopped the collaboration.

Nuno told Britain's Daily Star newspaper: 'I think the label had a seizure so they went down another route.'

However, Rihanna was joined by Nuno on stage at her London show at the 02 Brixton Academy on Monday night (16.11.09) and after the performance he was honoured to join her.

The 43-year-old rocker said: 'I've been asked to play with pop artists in the past but turned them down because they didn't really get the vibe. But when I spoke to Rihanna she was totally into transforming herself into a heavy rock chick.'

At her after-party at London nightspot Mahiki on Monday, Rihanna partied with boy band JLS, singer Mr Hudson and Chipmunk.

She said: 'I love British guys, they are so sweet. And the ones here tonight are so talented.'

The concert was Rihanna's first live show since she was assaulted by then-boyfriend Chris Brown in February.