British pop star Jessie J had a birthday to remember on Thursday (27Mar14) as music legend Sir Tom Jones took to the stage to perform with her at a special gig in London.

The Price Tag singer announced the acoustic concert in east London just hours before showtime and fans were let into the Oslo Hackney venue on a 'first-come-first-served' basis.

Jessie J put together the show to mark her 26th birthday and she had reason to celebrate when a special guest agreed to share the stage with her.

Jones, who worked with the singer on the U.K. version of The Voice singing series, wished his friend a happy birthday before joining her for a rendition of a song called Mockingbird.