And Haye admits he was impressed with his opponent's punching skills, writing in a post on his Twitter.com page, "Great workout in The Hayemaker Boxing Gym, Justin Bieber. You sure can pack punch!! I'm now a Belieber! Stay Blessed!"
Meanwhile, Justin gushed, "Worked out with Boxing Heavyweight Champion of the World David Haye. I took it easy on him. haha. good times (sic)."
It's not the first time the boxing giant has taken on a pop heavyweight - he sparred with rapper Dizzee Rascal earlier this year.