Mauboy, who was a runner-up on Australian Idol in 2006, struck up a close friendship with the Bridesmaids star and she was only too happy to perform at his August (12) nuptials to Tv presenter Dawn Porter.
She tells Britain's Daily Mail, "I'd seen Chris in Bridesmaids, so I was thrilled to find out he'd been cast. I was quite nervous when I first met him. I knew I could sing but I've never been to acting school so I was worried I might not measure up. But Chris put me at ease.
"I was at a party in Cannes when Dawn suddenly approached me. She was stumbling over her words, which wasn't like her. Finally, she managed to blurt out: 'You don't have to if you don't want to but I'd really love it if you would sing Chris and me down the aisle.'
"I couldn't believe it. She gave me a short list of songs to choose from and I immediately went for Halo by Beyonce."