Sir Tom Jones teamed up with Jessie J at an acoustic gig last night (March 27).

The 'Price Tag' singer took to the stage at the small Oslo venue in Hackney, London to celebrate her 26th birthday.

The move surprised fans as the concert was announced on the day - but gig-goers got another shock later in the night.

Jessie J's former Voice UK colleague Sir Tom Jones reared his head to sing the duo's collaboration 'Mockingbird'.

Speaking previously on Instagram about hitting 26 meanwhile, Jessie J said:

"This year I want to do things I said I would never do! Yes! I'm prepared for it all! Start living more for me! Going against MY grain!

"Time to experience life out of my comfort zone! And not caring what anyone else thinks. Enjoy being a grown woman! It's going to be an amazing risky and unforgettable year."

Watch Jessie J perform at her gig below: