Sam Smith has admitted recording a duet with Renee Zellweger for the soundtrack of upcoming movie Judy was a "career highlight".

The 27-year-old singer is a massive fan of the late Judy Garland, who Renee portrays in the upcoming biopic. So getting the opportunity to sing the iconic Get Happy was a no brainer for the Promises star.

"She (Judy) was one of the bravest humans out there and her vulnerability and honesty in her art still gives me goosebumps like it did the first time," Sam said. "It was truly an honour to sing with Renee. Nobody could have played Judy as well as Renee, and it is a career highlight for me to be singing with her - and, in some small way, with Judy."

The duet appears on the soundtrack album, due out on 27 September, with the record also including a rendition of Have Yourself A Merry Little Christmas by Renee and Rufus Wainwright.

"Judy Garland has been a constant force in my life. The Wizard Of Oz was one of the pyramids of culture that I gazed at as a small child," Rufus said of his admiration of the late star, who died in 1969.

Judy debuts in cinemas next month.