The longtime friends are together on a tropical vacation with Bieber's father and siblings, and the photos prove they're looking good and having fun.
From exploring beach ruins to sharing hair-ties, it appears the "Sorry" singer and Baldwin, whose father is actor Stephen Baldwin, are enjoying each other's company before the new year starts.
In one photo, Bieber had his hair pulled tight into a man bun and walked around some beach debris with only athletic shorts and Vans sneakers on. Baldwin, barefoot, stood nearby in only an oversized t-shirt.
Bieber's new look was thanks to Baldwin – in another Instagram picture he borrowed her hair tie to pull up his growing locks.
"I'll take that," he wrote.
Later, on Tuesday, the 21-year-old posed in front of a pool and beachside sea scape wearing printed swim trunks, orange sandal slides and an Eazy-E t-shirt.
"The boyz r back in town," he wrote, referencing his little brother Jaxon, who could be seen in the background.
Jeremy Bieber, Justin's father, was on the enviable trip, with daughter Jazmyn also in tow.
"Love you with all of my heart pops," Bieber wrote of a photo with his dad.
While the trip was certainly about family time, Baldwin and the star appeared to still find time for flirty fun.
In a video, shared by Bieber, the Canadian crooner looked mischievous as he licked his finger and stuck it in the unsuspecting model's ear.
"She thought we were taking a photo," he wrote.
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The longtime pals are used to romance rumors and, at least earlier this year, were not an item.
"We're just friends. I've known him for a long time, since I was about 13," Baldwin told E! in February. "He's just going through a time in his life where he's transitioning in a really positive way and he needs good people around him. And I'm trying to be a good friend and be there for him and support him."