Sara Bareilles performed 'She Used To Be Mine' live ahead of joining the cast of Waitress in the West End.
Bareilles, who composed the score for the hit musical, will join the London company from January 27.
She will play the lead role of Jenna alongside Gavin Creel in the role of Dr Pomatter.
Ahead of her first performance at the Adelphi Theatre, Bareilles belted out Waitress' hit song 'She Used To Be Mine' during an appearance on The Graham Norton Show on BBC One.
You can watch Sara Bareilles singing She Used To Be Mine below...
Bareilles and Creel - who were previously in the show on Broadway together - will appear in the West End cast through to March 7.
They will takeover from Lucie Jones and David Hunter who will return to their roles on 9 March.
It'll be Bareilles' West End debut while Creel previously appeared in the London casts of Mary Poppins and The Book of Mormon.
Bareilles said of joining the cast in London previously: "I am so excited to be using my passport in the New Year because I am coming to the West End to play Jenna in Waitress The Musical.
"I am coming to London and I am bringing one of my very best friends, Mr Gavin Creel who you would know from the original cast of the Book Of Mormon."
Waitress tells the story of Jenna a waitress and expert pie-maker who dreams of a way out of her small town and rocky marriage.
Alongside Bareilles' score, the hit musical features a book by Jessie Nelson and direction by Diane Paulus.
Waitress in London recently announced it would be playing its final performance on July 4 ahead of a first UK tour.
The standard performance week is Monday to Saturday at 7:30pm with Wednesday & Saturday matinees at 2:30pm.