The 43-year-old country star performed at the Forum as part of his Friends and Heroes Tour on Saturday night, where an eyewitness tells ET he and Stefani looked more in love than ever.
Stefani, who attended the show with her sons, 13-year-old Kingston, 11-year-old Zuma and 6-year-old Apollo, also got up on stage to sing "Nobody But You" with her boyfriend of four years -- surprising the audience about an hour into Shelton's set. The blonde beauty stunned in a denim and diamond fringe look, which she paired with thigh-high sparkly boots. The custom Daniel Diamond jacket had "Blake" embroidered on the back.
"When Gwen took the stage, the entire audience erupted in screams and cheers," ET's eyewitness shares.
Following their performance, the happy couple showed off some PDA. "Blake was kissing Gwen's cheeks while they were hugging and laughing," the eyewitness adds. "It was the cutest thing."
Stefani enjoyed the rest of the show with her sons, as they cheered Shelton on from the side of the stage. The former No Doubt singer -- whose mom was also in attendance -- shared a cute snap of her and Shelton with her boys.
In a December interview with ET, Shelton opened up about collaborating with Stefani on "Nobody But You," revealing that she was "crying when we even just talked about singing it together at all."
As for their relationship blossoming after their respective divorces, Shelton said that it wasn't "an accident."
"Both of us know that the timing, and the way she and I met and came together, it just felt like home, that's not an accident," he said. "I think that the way that she and I were able to save each other's lives and get ourselves through that time it was evidence to us that God had a hand in it."