The "Record Year" hitmaker admits he was always nervous to tackle "The Star-Spangled Banner" because he doesn't think he has the vocal ability to pull off the tune, but after hearing Sullivan sing, he jumped at the opportunity to collaborate with her.
In an interview on Apple Music Country, Church admits he came close to turning down the Super Bowl invite.
"Let me tell you something. She may be the best singer. I was floored," he gushed in the chat, which is set to premiere on Friday, January 29.
"And you know what, the best thing about this, no matter what happens, because that's a nervy thing that we got to do, but what a fan, I'm a fan (of Sullivan's). I've went in and listened to everything she did (sic). And I had heard her name, but full disclosure, I had not listened (to her songs)."
The unlikely duo, which has yet to meet, was suggested by producer Adam Blackstone, and prior to hearing Sullivan's work, Church wasn't that keen, reports People.com.
"Here's what I said... I've said this forever, 'I will never ever sing the national anthem.' It's so hard. Except (for) the Super Bowl...," he shared. "I mean, I'm not Chris Stapleton. I fully assumed they're never going to ask me. So, this is the first."
"My first response was, 'Mm-mm. I'm a stylist, not a vocalist,' " he added. "I heard it (duet proposal) and I thought, 'That's cool, that sounds like me.' And then I heard her (Sullivan) and I'm not missing a chance to sing with her. And that was it."
"Once I heard her voice, I said, 'OK, I'm in.' "
The duet partners will be hitting the stage together in Tampa, Florida on 7 February, when the Tampa Bay Buccaneers will take on the Kansas City Chiefs for the Super Bowl title.
The Weeknd will be performing the Super Bowl Halftime Show.