The 63-year-old British singer, who recently welcomed a son with partner David Furnish, met Gaga at a charity ball and said they have been firm friends ever since.
Speaking to Access Hollywood, he said, 'We became friends, and I adore her. I told her about the song, and she said, 'I'd love to do it', and she did it. We're just so thrilled she took time out of her incredibly busy schedule to do it.
'She had fun with it and changed it a little bit and brought her own personality to it, so she gave Juliet that personality.'
Hello, Hello will be released on February 8.