London: Pop sensation Lady Gaga says her decision to pose nude for legendary crooner Tony Bennett as he sketched her was one of her most "nerve-wracking" moments.

The 'Bad Romance' singer was persuaded to disrobe for Bennett - an acclaimed artist, by photographer Annie Leibovitz for a Vanity Fair photoshoot with the pair who teamed up to record a duet, according to reports.

"True to form, as me giving my all to my work (sic), I walked in and I said, 'Well, Tony, here we are...' and he started laughing and I dropped my robe and I got into my position. It was very, very nerve-wracking.

"I felt shy, it's Tony Bennett. Why am I naked...? The first thing that Tony said to me when I saw him (afterwards) was, 'Wait 'til you see this sketch I did. It's amazing. You look beautiful,'" she said.

And the 25-year-old singer admits it was a huge moment in her career because the 'I Left My Heart in San Francisco singer' is such a legend to her.

The sketch and the Leibovitz photo session appears in the January issue of Vanity Fair magazine.