Sir Paul McCartney was so wracked with nerves while recording tracks with jazz star Diana Krall, he was convinced he'd "disgraced" himself and was "rubbish".
The Beatles legend has covered several classic standards for his new album, Kisses on the Bottom, and he recruited Krall and her backing band to provide the music.
It's the first time MCCartney has ever performed vocal duties without playing a guitar, bass, or piano at the same time - and the experience was so daunting, he quickly felt out of his depth.
MCCartney tells Culture magazine, "Here was I in this completely new role, feeling really quite intimidated. There was nothing to hide behind, no guitar or piano that I could put between me and 'it'. I had to sort of find a vocal style...
"I'm in front of really good musicians, who know what's going on, and I'm thinking, 'Bl**dy hell, I'm going to totally disgrace myself here. I'm going to be, like, the worst person in this band, and I'm supposed to be, like, not bad. They're all going to be smiling at me, but secretly thinking, Jesus Christ, this guy is rubbish.' Then I think, 'Get it together, MACca, come on.'... So, yeah, me not having an instrument was very strange, very intimidating."