Fans had speculated for months that the couple were engaged after the singer showed off an incredible diamond ring during her holiday in Capri, Italy.
And it turns out they were right because Lily and David exchanged vows in Las Vegas on Monday!
But what do we know about her romance with the American actor? Keep reading to find out...
WATCH: Lily Allen's daughter's amazing voice will surprise you
Lily and David Harbour have been linked since August 2019
When did Lily Allen and David Harbour first meet?
The 35-year-old pop star and David, 45, surprised fans when they were spotted together at a West End production of The Lehman Triology in August 2019. A string of dates ensued, including a boxing match and several PDA-filled outings.
The pair were seen publicly kissing at Madison Square Garden in October, proving things were getting serious.
David and Lily only made their official red carpet debut in January of this year, attending the SAG Awards 2020 arm-in-arm. They sure make an attractive couple!
David flew from New York to London to spend lockdown with Lily
Do Lily Allen and David Harbour live together?
The pair have spent most of their relationship on different continents, dividing their time between the UK and David's New York City apartment.
During the coronavirus pandemic, David moved into Lily's London home with her children Ethel, eight, and Marnie, seven, who she shares with ex-husband Sam Cooper.
David had been in Atlanta filming Stranger Things, but managed to fly out to the UK to see Lily just before travel restrictions kicked in, admitting it would have been a "really bad situation" for his mental health "to be quarantined alone".
Lily has been showing off her ring for months
When did Lily Allen start wearing an engagement ring?
Rumours first began circulating that David had popped the question after Lily was spotted wearing a ring during a stroll around Chelsea, London in late November.
Her fans have also quizzed her about it on Instagram, but the British singer has always refused to comment.
Responding to a direct fan question, she joked: 'First rule of engagement club........,' referencing Brad Pitt's famous line from Fight Club ("you do not talk about Fight Club").
This could be Lily's second marriage; she separated from husband Sam Cooper in 2015 after about four years of marriage, before finalising their divorce in 2018.
The couple have made a few low-key public appearances
What is David Harbour best known for?
David is perhaps best known for his role as Jim Hopper in Netflix's smash hit show Stranger Things. The no-nonsense police chief makes it his mission to find missing local boy Will Byers – only to get sucked into the dark and mysterious world of the Upside Down.
Aside from fighting Demogorgons, David is also famed for playing the titular anti-hero in Hellboy. The talented actor has also starred as Gregg Beam in Quantum of Solace, Shep Campbell in Revolutionary Road and Dexter Tolliver in Suicide Squad.
David previously dated Fantastic Beasts star Alison Sudol
Who are David Harbour's exes?
You might recognise some of David's famous exes! The star was previously in a relationship with Fantastic Beasts And Where To Find Them actress Alison Sudol.
David and Alison, who also performs under the name A Fine Frenzy, called it quits a few months before he was linked to Lily.
The actor was previously rumoured to be engaged to Forgetting Sarah Marshall star Maria Thayer. However, the pair quietly ended things in 2011 before they were allegedly set to walk down the aisle.
In other surprising news, he also dated Julia Stiles for four years between 2011 and 2015 – and they even lived together in New York! Who knew!
When did Lily Allen and David Harbour marry?
Lily and David were married by an Elvis impersonator
Lily and David exchanged vows at the Graceland Wedding Chapel, with the ceremony carried out by Brendan Paul, an Elvis impersonator who owns the chapel.
The couple are in good company, as Jon Bon Jovi and his wife Dorothea held their wedding there, while Billy Ray Cyrus and actress Andie McDowell are among those who have renewed their vows at the chapel.
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