Despite the pair's now-inseparable nature, Shelton revealed that when they were first filming The Voice together, they didn't talk all that much.
"I didn't really know her that well, the first time around," the country singer said. "Just "hey, how're you doing," you know."
But when Shelton found out that Stefani was going through a divorce with her ex-husband, Gavin Rossdale, at the same time Shelton was splitting from Miranda Lambert, everything changed.
"When my marriage fell apart, and then trying to pick the pieces up from being at the rock bottom and trying to move forward, next thing you know, there's this person that I kind of knew, that I worked with on [The Voice]," he said, "And then all of a sudden, to find out she's going through the same exact thing at the same time."
"This is how my life turned around. And so quickly too, by the way. Like, all of this has to be meant to happen. So I made a record about it," he added, referencing his new album, If I'm Honest.
And when Handler asked Shelton if this was the happiest he'd ever been, he replied, "There's no question about that. Absolutely no question about that."
The full episode of Chelsea will stream on Netflix July 6.