The 30-year-old singer and producer, who is working on songs for his forthcoming album, described the experience as "surreal", reported Digital Spy.
"The first time I worked for her I wrote a song for her, which in itself was surreal," he said.
"This time around I actually did a duet with her - it's her and me on one song, which was a challenge to say the least! I was trying to figure what I was even doing there - why would they need my voice when they have hers?"
Dion's forthcoming album - tentatively titled 'Water and Flame' - follows 2007's 'Taking Chances' and marks her tenth English album.
