The couple have been dating since 2015 after meeting on the NBC series "The Voice."
"Cheers to new beginnings and unapologetically walking in your truth," he told fans in his announcement, which also marked his 25th birthday.
"I lost all my breath when they announced my name," the winner said.
On "The Ellen DeGeneres Show," the Maroon 5 frontman said he's having the "greatest time" after moving on from NBC's talent competition series.
Shelton says he'll miss trash talking the Maroon 5 singer, something he can't do with new judge and girlfriend Gwen Stefani.
Gwen Stefani will replace the Maroon 5 frontman in the new season.
The model faced backlash after sharing tweets from the NBC show's official account. She responded tongue-in-cheek.
The 26-year-old Texan gave coach John Legend a victory in his first season on the singing competition.
The powerhouse crooner, who was featured on "Team Miley" during the singing contest's 13th season, died Saturday after battling "extreme" pneumonia.
The singer's surprising victory wraps up the NBC talent show's Season 15.