The pair worked together on 1998 film The Object of my Affection, and 2012 romcom Wanderlust, and have remained firm friends.
But to celebrate Paul's 52nd birthday, the Friends actress was quick to joke about how the Ant-Man star is seemingly incapable of aging.
WATCH: Jennifer Aniston showcases her morning routine in figure-hugging outfit
Alongside a still from the film, Jen wrote: "You don't seem to age which is weird - but we celebrate you anyway!"
In a second story on Instagram, Jen shared two pictures from a 2012 GQ photoshoot which saw them in bed together and having a pillow fight.
"I love you," she captioned the story while a third featured a video from their film.
They worked together in 1998 film The Object of my Affection
Paul has also worked with Jen on her 90s comedy Friends, but in 2019 opened up about getting off on the wrong foot - literally - with the actress.
Chatting on the Graham Norton Show the star admitted that he accidentally made a huge faux par with the actress, who famously played Rachel Green in the popular sitcom.
They reunited on screen in 2012
He explained: "I was on the set for my first episode and Jennifer was on a Segway because she had broken her toe, and everyone was marvelling at it.
"Matt LeBlanc asked to have a go and immediately knew how to do it. I then asked to try it too. I spun round and rolled it right over Jennifer’s foot!
"The producer's look of panic was if to say, ‘Is it too late to fire him? Has his character been established yet?’ I felt awful. Such an inauspicious start."
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