Gwen Stefani & Blake Shelton 'Still Act Like Lovebirds' as They Return to The Voice Together

Ahead of their four-year anniversary, Gwen Stefani and Blake Shelton are returning to the stage where they had their meet-cute.

The couple is back to work together on The Voice set as the mother of three, 49, makes her return as a coach following the departure of Adam Levine, who announced his exit in May after 16 seasons.

“They’re coming up on their four-year anniversary, but Blake and Gwen still act like lovebirds,” a source tells PEOPLE of the pair, who began dating in fall 2015 while both starring on the NBC series.

“They’re really happier than ever, and being back where they first fell in love has been fun for them,” the source says. “They can’t believe how quickly time has flown by, and their relationship is very solid. Blake worships her, and Gwen feels very secure with him.”

RELATED: Blake Shelton Talks Marriage Plans with Gwen Stefani: ‘We’ve Never Been Doing Better’

Blake Shelton and Gwen Stefani. | John Shearer/ACMA2019/Getty
Blake Shelton and Gwen Stefani. | John Shearer/ACMA2019/Getty

Four years later, Stefani and Shelton are co-workers once again, this time joined by fellow coaches Kelly Clarkson and reigning victor John Legend.

“It’s like she never left,” the source says of Stefani’s Voice homecoming, adding, “Her kids also love going to set.”

Stefani first appeared on the singing competition in late 2014 for season 7 with fellow newcomer Pharrell Williams. The former No Doubt singer, who replaced Christina Aguilera, would go on to coach seasons 9 and 12.

RELATED: Gwen Stefani Says Blake Shelton Is Her ‘Best Friend’ as She Opens Up About Returning to The Voice

Recently, Shelton told PEOPLE about how quickly he and Stefani’s time together has passed since they were first romantically linked.

“It’s actually shocking that it has already been that long,” he said in June. “It’s kind of a blur. It still feels like it’s pretty new to me. I guess it is, relatively. Four years isn’t forever, but man, it seems like it just happened in no time.”

Trae Patton/NBC/NBCU Photo Bank/Getty
Trae Patton/NBC/NBCU Photo Bank/Getty

And when it comes to The Voice, the country singer knows his girlfriend is a tough competitor. “This will be her fourth time on the show, so she’s no stranger to it. She knows what she’s doing,” he said.

“I’m glad that she’s already feeling competitive. Of course, I’m not going to let her win. I’m going to have to win, but I’m going to have to do it in a way that she doesn’t feel like I beat her,” Shelton continued. “I don’t know if that’s possible or not because I definitely don’t want to upset her — that’s not going to pay off for me in the long run.”

Season 17 of The Voice will premiere on NBC on Sept. 23.