"So, Blake told me y'all are engaged now," DeGeneres bluffed. "Yes, he told me you're engaged, so let's talk about that."
"No, we're not!" Stefani responded. "What are you talking about? We're not. We're not engaged. We're not married. And he's my boyfriend... still."
Stefani couldn't help but gush about Shelton, who was succeeded by actor Idris Elba as People's Sexiest Man Alive this year.
"Honestly, he got sexier," she said of Shelton losing the title.
DeGeneres kept pushing the "You Make It Feel Like Christmas" singer, asking if Shelton got better in bed once Elba was named Sexiest Man Alive.
"Oh my God!" Stefani responded before telling the audience, "I feel like she needs to try to take it to the next level every time I come with Blake."
Stefani and Shelton confirmed their relationship in November 2015 following their respective splits from Gavin Rossdale and Miranda Lambert. Shelton said in an interview with Today in June that he's closer than ever to Stefani.
"Now here we are, going on three years later and every day that goes by, it just feels like a stronger bond between the two of us," the star said.
"It constantly feels like it's going to the next level. That's the only way I think either of us could probably describe it," he added.
DeGeneres similarly teased singer Jennifer Lopez about Alex Rodriguez during an episode of Ellen last week. Lopez confirmed she's "very happy" with the retired MLB star but said she isn't sure if they will wed.