The Star Trek actor has been known to dabble in music, and previously showed off his vocal ability in Rob Marshall’s 2014 musical fantasy film Into the Woods.

But the 35-year-old wasn’t so confident when Hollywood icon Barbra asked him to sing with her on her forthcoming album Encore: Movie Partners Sing Broadway, which also features appearances from seasoned performers such as Anne Hathaway, Hugh Jackman and Jamie Foxx.

For the record, Chris sings a version of I’ll Be Seeing You from the 1938 Broadway musical Right This Way, but when it came to performing the song he was so worried about his ability that he found it difficult to concentrate on the task at hand.

“I don’t even remember (singing the song),” Chris said during an interview on Jimmy Kimmel Live! on Monday night (01Aug16). “I was terrified... She was like, ‘Of course you know this (song)’ and I was like, ‘I don’t Barbra, (but) you could give me four lines out of the phonebook and I’d sing it with you.’”

Though Chris was keen to meet with Barbra, 74, so they could sing together, he admits that work conflicts meant he recorded his part in London, while she laid the track down in Los Angeles.

But Chris was happy it worked out that way, as it took less pressure off of him to perform on the spot.

“She was in L.A. and I wanted to sing it with her, like 50 per cent of myself wanted to sing it with her, 50 per cent was like maybe I shouldn’t because I’d like to try and do a good job,” he shared, humbly adding that he wasn’t by any means the star of the song. “I’m casually trying to throw in little glimpses of OK-ness amidst the Barbra.”

Encore, which will be Barbra’s thirty-fifth studio album, is set to be released on 26 August (16).