Blake Sheltonis showering girlfriendGwen Stefaniwith nothing but love on her milestone 50th birthday.

On Thursday, the country star paid tribute to the No Doubt singer with a sweet message on Twitter. “Happy Birthday @gwenstefani!!!! I love you so much it’s actually stupid… And possibly illegal in the state of California,” Shelton wrote.

Next month, Shelton, 43, and Stefani will celebrate another milestone: their four-year anniversary of dating. The pair first met on the set ofThe Voicein 2014, and seven months later — after both of their respective divorces (Shelton from fellow country starMiranda Lambertand Stefani fromGavin Rossdale) — they sparked up a romance.

“It’s actually shocking that it has already been that long,” Shelton toldPEOPLEin June of their upcoming anniversary. “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.”

In celebration of Shelton’s birthday in June, Stefani threw him an epicpizza partyat her house and gifted him a huge customwelcome signto put on display at his Oklahoma ranch. Additionally, Stefani’s sons Kingston, 13, Zuma, 10, and Apollo, 5 (whom she shares with Rossdale, 53) also wrote out birthday cards for him.

“Christmas, birthdays, any kind of holiday — they always sit down and take time to write a message and draw pictures or something,” he said. “Those are the coolest, coolest things, you know? It’s something I never experienced in my life. When they take time and actually make something, it’s pretty cool.”

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gwen-stefani

Ahead of his birthday, Stefani also shared a tribute to Shelton onInstagram, affectionately calling him her “favorite human.”

“Can’t believe [you’re] mine ❤️🤷‍♀️ #soooooolucky!!!!” she wrote alongside a slideshow of throwback and more current photos of Shelton, including several shots of them cuddling up together.

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Gwen Stefani and Blake Shelton

Last month, Shelton told PEOPLE that having Stefani back on set has helped with “the weirdness” of Levine, 40, not being there.

“He’s never not been here, you know?” he said. “And it’s just that guy that’s just over there constantly just makin’ you want to strangle him. And now he’s gone and it sucks, to be honest with you. But havin’ Gwen back, for me, makes it a lot more fun.”

RELATED VIDEO:Blake SheltonMisses Adam Levine on ‘The Voice’ butGwen StefaniHelps Make It ‘Fun’

As to whether he and Stefani tend to take their work home with them, Shelton said, “It’s impossible to not.”

“We’re onThe Voicetogether, so obviously, if something crazy happened, we’re still going to be talking about it when we get home,” he said. “And a lot of pillow talk about our artists and stuff.”

Blake Shelton and Gwen Stefani.Trae Patton/NBC/NBCU Photo Bank/Getty

The Voice - Season 12

According to Shelton, Stefani is “taking 100 percent advantage” of the fact that he has a soft spot for her this season. For example, Clarkson, 37, noted Stefani has said, “Blakey, I want this one,” on the show when going head-to-head with him for an artist they both want on their teams.

“I’m going to fight for people that I think are great,” Stefani said. “If that means having to fight Blake hard, I’m gonna’ do it.”

Stefani went on to say that every season of she has worked with Shelton have been “completely different because I’ve been in different places in my life.” But, “this time’s my favorite because we know each other so well,” she said.

Along with her work onThe Voice, Stefani will continue performing herLas Vegas residencyshows at the Zappos Theater through Nov. 2.

source: people.com