The music mogul recently claimed he would have all his acts perform when he weds girlfriend Lauren Silverman and his 'X Factor' protegee - who shot to fame in 2006 with Cowell's guidance - believes he would make her sing the hit ballad, which she recorded in 2009, reported Contactmusic.
"He'd probably get me to sing 'Happy' because I think that's one of his favourites of my songs," Lewis said.
The track is about taking chances no matter the potential risk, with lyrics including: 'I gotta find my place, I wanna hear my sound, don't care about all the pain in front of me, 'cause I'm just trying to be happy.'
"It's so weird. I never thought I'd see the day but I think it's amazing. It's so lovely having a baby. I'm so happy for him," Lewis said.