Joe Jonas rocked a very interesting choice of attire on Friday while attending the U.S. Open with brother Nick Jonas.
As the two brothers watched Rafael Nadal take the court, Joe, 30, was photographed wearing a Justin Bieber shirt, which depicted the Canadian pop star wearing Jonas Brother apparel.
The image portrayed on Joe's shirt appeared to be taken from one of Bieber's outings over the summer, when the 25-year-old singer was spotted in West Hollywood wearing a shirt with a throwback photo of the group on it, which was from his own clothing line, Drew.
Although Joe's choice of apparel could be a sign of the pair's mutual affection for one another, it could also be a sign that Bieber has become the latest celebrity to join the Jonas brothers in a light-hearted prank war.
In February, Nick, 26, kicked off a prank war with actor John Stamos, who had been spotted several times over the years wearing Jonas Brother T-shirts.
Taking notice, Nick stepped out wearing a sweatshirt that had a photo on it of the Fuller House star wearing a JoBros T-shirt.
"It's your move @johnstamos," he wrote, sharing the photo on Instagram.
Stamos quickly hit back by creating a pillow with a photo of Nick' sweatshirt on it - which Nick proceeded to get made into a large blanket.
Escalating things even further, the You actor even appeared to get an apparent tattoo of Nick's face on his arm. "#jobrosforlife," he captioned an Instagram photo of his tattoo artist getting to work.
Stamos even got Joe in on the fun after the actor chimed in with his own extra special song request.
Before the group embarked on their Happiness Beings tour earlier this year, Joe made a post on Instagram asking fans which songs they'd most like to see the group perform.
Choosing a number that's very much outside their repertoire, Stamos suggested "Forever!" a reference to the Beach Boys classic his character Uncle Jesse sings to his wife during their wedding ceremony.