Gomez, 30, and newlyweds Beckham, 23, and Peltz, 27, celebrated the holiday with a getaway to Los Cabos, Mexico.
But Gomez’s most recent post has displayed just how close their friendship has become in just a short space of time.
Find out more about Selena Gomez’s relationship history in the clip below…
The ‘Lose You to Love Me’ singer took to Instagram in January and shared a number of photographs from the New Year trip, including one of the three snuggled up on a flashy boat.
The other snap showed the trio embracing as they laughed their way into the new year.
“Fine call us a throuple #foreverplusone,” the post was captioned.
In a separate post, Gomez and Peltz were also shown getting ready for their big New Year’s Eve celebrations.
In the photo, the pair were seen wearing matching sparkly silver Valentino dresses.
“Thanks @maisonvalentino for me and my angels’ dresses,” Gomez wrote.
Commenting on the post, Peltz gushed: “I love you my angel forever!!!”
And if anyone was left in any doubt about Gomez and Peltz’s friendship – they doubled down by displaying matching ‘angel’ tattoos in an Instagram story on Monday.
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Fans were quick to jump on Gomez’s ‘throuple’ comment, with one joking: “If she can’t get a significant other the rest of the single population is screwed!”
Another fan wrote: “Could y’all imagine somehow meeting Selena and becoming her best friend?
“Like it’s literally my dream. I cannot imagine how much fun they have.”
“Selena Peltz Beckham Gomez, yes!” added a third.
While a fourth commented: “Third-wheeling never looked so good.”
As Brooklyn Beckham chose to spend the festivities with his wife and friends, Victoria Beckham noted Brooklyn’s absence in her Christmas Instagram post.
Showing David Beckham wearing matching pyjamas alongside Brooklyn’s three siblings, Romeo, 20, Cruz, 17 and Harper, 11, she wrote: “Dad keeping up the family tradition.”
Mentioning her eldest son, she said: “We love you and miss you.”
Since getting married last spring, Peltz’s relationship with Brooklyn’s mum has been heavily scrutinised.
There had been rumours of a bust-up over her wedding dress – which was not designed by Victoria – in the run-up to the wedding, but Peltz decided to clear things up in the summer.
She told Variety: “I was going to [wear it] and I really wanted to, and then a few months down the line, she realised that her atelier couldn’t do it, so then I had to pick another dress.
“She didn’t say you can’t wear it; I didn’t say I didn’t want to wear it. That’s where it started, and then they ran with that.”
Watch our Video of the Day below…