Gwen Stefani: I didn't even know Blake Shelton existed before 'The Voice'

Gwen Stefani and Blake Shelton famously fell in love while filming "The Voice." And it's a good thing they met on the NBC stage, because before joining the show, Stefani had absolutely no clue who Shelton was!

"I didn't even know that Blake Shelton existed in the world!" the star revealed on Tuesday's "Late Night with Seth Meyers." "I had no idea."

Even as the two got closer and closer, Stefani admits she still didn't know what Shelton's voice sounded like -- even though she'd heard him perform live! When Shelton asked her to collaborate on a song, Stefani felt "super awkward" to hear what he'd already produced.

"He sent me this song in an email, and I was so scared because at that point I really didn't know even what his voice really sounded like," Stefani said. "Like, I'd heard it on the show, but I wasn't paying attention. I was like, 'Whatever, country guy's on. When's Pharrell coming on?'"

See photos of Gwen Stefani and Blake Shelton:

Even though Shelton is an award-winning artist and one of the most popular country singers of all time, Stefani was skeptical: "I was like, 'What if I hate this song?!'"

After some deliberation, Stefani bit the bullet and listened to the track. It was "Break My Heart."

"I wrote a verse back to him ... and then we had this song, and it's been incredible because we get to hop on each other's stages," Stefani said. "I can be at one of his country shows and come up and sing that song, and he's come up on my stage -- which is just so bizarre. He comes out there, and it's like, what are you doing here? Who are you?'"

Of course, Stefani has since made up for her Shelton-related ignorance: "Trust me, I'm the biggest Blake Shelton fan ever now. I know all of his music."

She added, "Cross-pollination of music is pretty special."

"I'm glad you said 'of music,'" Meyers quipped.