The couple obtained their marriage license in Las Vegas. According to The Daily Mail, they said "I do" at the Graceland Wedding Chapel in Vegas, and the ceremony was officiated by an Elvis Presley impersonator.
ET reached out to Allen's rep for comment, though they had no comment.
This marks Harbour's first marriage. Allen was previously married to Sam Cooper, but their divorce was finalized in 2018 after seven years of marriage. They share two kids: 8-year-old Ethel and 7-year-old Marnie.
The "Smile" singer and the Stranger Things star have been romantically linked since last October, when they were spotted kissing in New York City. They later made their red carpet debut as a couple in January at the 2020 Screen Actors Guild Awards. In March, Harbour made headlines after he called Allen his "wife" on Instagram Live, though she quickly clarified that they weren't technically married.
By May, Allen all but confirmed they were engaged when she responded to a fan asking if she was sporting an engagement ring in her Instagram photos. "First rule of engagement club," she quipped in her reply, referencing the Fight Club movie line about not talking about Fight Club.
Meanwhile, Allen recently shared pictures from the family vacation they took in Croatia.
Harbour also recently shared sweet pictures of him spending time with his now stepdaughters on Instagram.
For more with Harbour, watch the video below.