The Angels hitmaker is working on a follow-up to his hit 2001 cover album Swing When You're Winning, which featured renditions of MACk the Knife, Mr. Bojangles and Somethin' Stupid, which he recorded with Nicole Kidman.
Now Williams has collaborated with Buble, who is no stranger to covers of swing classics.
The Cry Me A River singer tells Britain's Daily Star, "I got to know Robbie through (the U.K. version of) The X Factor and I love him. The song is for his new swing album and it's so good. We had too much fun making it."
And Buble admits he and Williams bonded over their struggles with dealing with fame, adding, "Robbie has probably been more open than I have with certain things. I'm pretty open but he's bared his demons. I have the same demons, so we talk about all the things I think about as I don't have other people to talk to them about. It's pretty awesome."