"I love Blake! He is the most incredible guy. Everybody loves Blake and that’s the thing, there's no way around it, he's just a sparkly, happy amazing person," Stefani told Seth Meyers on Tuesday's Late Night. "[But] he is in trouble this season. I'm about ready to get on him."
Shelton has won five times in 11 seasons, making him the most successful Voice coach by far -- but Stefani seems intent on making sure he doesn't earn his sixth title this time around, joking that there's already been some tension between them this season.
"He's been on the couch a few nights so far," she quipped.
Stefani also opened up about how, before their relationship, she wasn't very well acquainted with country music at all, and she "didn’t even know that Blake Shelton existed in the world."
However, things have change pretty dramatically in the last few years, and the 47-year-old No Doubt frontwoman says she's "the biggest Blake Shelton fan ever now. I know all of his music."
Her appreciation for his songs, and his love for her music, has afforded the cute couple the opportunity to get really involved in each other's careers, and allowed them to show their support while they are on tour and performing live.
"It's been incredible because we get to hop on each other's stages and I can be at one of his country shows and come up and sing… and he can come on to my stage," she shared. "It's been magical because cross pollination of music is pretty special."
While she had no problem poking gentle fun at her beau, Stefani had nothing but effusive praise for the iconic Celine Dion, who is serving as her team's mentor on the upcoming season of The Voice.
"She is like, the ultimate person that you would want to be on there," Stefani marveled. "She is so unique…. Every song she puts out is a world song, she speaks to the world and that's a whole other level [than], 'Oh I made it as a pop star in America.'"
"She's [been] massive since she was 13 years old, so having her on the show was incredible," she added.
ET caught up with Dion in Las Vegas on Tuesday where she opened up about becoming a Voice mentor, and revealed what advice she would give to her younger self, knowing what she knows now.
"Be yourself and don’t be in competition with the world, be in competition with yourself," Dion shared. "And Don’t hold on to just one dream, because if you don’t make it are you going to tell me that this is the end of your life?... Life is more than a song, baby!"