The much-anticipated return of Gavin and Stacey achieved the best Christmas Day TV ratings for more than a decade, early "overnight" figures show.
The Christmas special was watched by a "well lush" average of 11.6 million viewers on BBC One.
When it went on air at 20:30 GMT, half (49.2%) of all TV viewers tuned in.
The episode, written by and starring James Corden and Ruth Jones, revisited Gavin, Stacey, Smithy and Nessa nearly 10 years after they left our screens.
The next most-watched programme was the Queen's Christmas Broadcast, which was screened on BBC One, ITV and Sky and seen by 7.85 million people.
In recent years, The Queen's annual broadcast has become the most-watched TV show, based on the overnight figures which do not include viewers who watch Christmas specials on catch-up services during the rest of the festive period.
Strictly Come Dancing, EastEnders and Michael McIntyre's Big Show - all on BBC One - rounded out this year's top five shows.
Charlotte Moore, Director of BBC content, said: "We delivered something for everyone with the seven most-popular programmes that cap off an incredible year for BBC One celebrating British talent and creativity."
by Lizo Mzimba, BBC entertainment correspondent
For the last few years the headlines out of the Christmas Day viewing figures have been pretty consistent - the Queen's annual address to the nation the most watched show as Christmas Day viewing declines year-on-year.
Gavin and Stacey have reversed that trend to such an extent that the cast's reactions have probably been a lot more vociferous than Nessa's "tidy" or even Stacey's "well lush"!
They and the BBC will be thrilled. It's proof that while terrestrial Christmas audiences have been decreasing, they're still there in huge numbers for the right kind of show.
So much of what's been offered on recent Christmas Days has been festive editions of programmes that are already regular fixtures in the schedule.
Gavin and Stacey's Christmas Special felt like real event, must-see TV; the first new episode of the award-winning, much-loved comedy for nine years.
And once catch-up viewing has been taken into account, it stands a good chance of, at almost the last gasp, overtaking the Line of Duty finale as the most watched programme of 2019.
The high viewing figures mean that there'll be a lot of expectation from audiences for more Gavin and Stacey, and (without giving away any spoilers) the door has been left enticingly open for that.
And if the BBC can persuade co-writers James Corden and Ruth Jones, there's little doubt that BBC One would love more Gavin and Stacey, too.
Gavin and Stacey, written by Corden, who plays Smithy, and Jones, who has reprised the iconic role of Nessa, first aired in 2007.
Corden revealed on Wednesday that he and Jones watched the special together, telling fans the show has been "a labour of love from start to finish".
We had to be together to watch it go out tonight!Gavin and Stacey is a show about friendship and family. Tonight’s show has been a labour of love from start to finish and we hope you enjoy it.Wherever you are and whatever you’re doing.Happy Christmas from us both #GavinandStacey pic.twitter.com/kUKMiXUEyL— James Corden (@JKCorden) December 25, 2019
Shortly after the episode aired, Rob Brydon, who reprised the role of uncle Bryn, thanked fans for their kind comments.
Thanks for your lovely Tweets. I'm having another Archers to celebrate.— Rob Brydon (@RobBrydon) December 25, 2019
The initial series saw the budding romance between Essex man Gavin Shipman, played by Mathew Horne, and Welsh woman Stacey West, portrayed by Joanna Page, flourish.
There were two subsequent series and a 2008 Christmas special.
It had been a decade since audiences left Gavin, Stacey, Smithy and Nessa sitting on the seafront on Barry Island, but the Christmas special proved these four - and their famous expressions - are still a big hit.
The special also saw Alison Steadman and Larry Lamb return as Pam and Mick Shipman, as well as Melanie Walters as Gwen and Robert Wilfort as Jason.
Many fans expressed their eagerness to see another series following last night's special.
Omg that was everything I hoped it would be, what a place to end it though😭 #GavinandStacey— lizzie🎄 (@lizziebarnettx) December 25, 2019
if they don’t make another season after that i’m gonna sue #GavinandStacey— ꪖꪶꫀ᥊ (@Alexsummers_x) December 25, 2019
Jones told BBC Newsbeat that "there isn't any plan, at the moment" for another Gavin and Stacey series, but did not rule it out in the future.
In the Christmas special, viewers only had to wait a few minutes to hear Nessa ask her infamous question "What's occurring?".
And of course, it wouldn't be a Gavin and Stacey special without a reference to that infamous fishing trip.
The success of Gavin and Stacey made Corden and Jones household names - even though they were not the Gavin and Stacey named in the title.
Since the original series Corden's career has skyrocketed in the US, with his hugely successful gig as host of The Late, Late Show.
Jones told the BBC that trying to find the time to film was challenging, with Corden recording episodes of his US show back-to back to give him to time to work with Jones on the British project together in LA earlier this year.
Top 10 most-watched programmes on Christmas Day 2019
1. Gavin and Stacey (BBC One) - 11.6m
2. The Queen's Christmas Broadcast (BBC One, ITV, Sky) - 7.85m
3. Strictly Come Dancing (BBC One) - 5.49m
4. EastEnders (BBC One) - 5.47m
5. Michael McIntyre (BBC One) - 5.25m
6. Call The Midwife (BBC One) - 5.23m
7. Mrs Brown's Boys (BBC One) - 4.63m
8. Coronation Street (ITV) - 4.48m
9. Emmerdale (ITV) - 4.11m
10. Finding Dory (BBC One) 3.99m