The legendary crooner is a huge fan of the 'Born This Way' singer and couldn't believe it when she accepted his request for the pair to record a duet.
He said: "She was so warm and friendly and sweet. I said, 'I'd love to make a recording with you.' And she said, 'Anything you want. I'll do it.' I was thrilled by her reaction, because she's in such great demand, so I didn't know what her response would be."
While he is a fan of the latest crop of pop stars, Tony, 85, says he owes his career to one man - the late Frank Sinatra.
Tony - who opened up The Sinatra School' in the 'My Way' singer's honour - said: "He changed my life. In an article in Life magazine, he was emphatic about saying that IO was the best singer he'd ever heard. I was moderately popular then, and every so often I would have a million-selling record, but for me it was about being good, not the most famous. Then he called me the best he'd heard. And since then, I sold out around the world. I thought naming the school after him was proper etiquette."