Acting as an anniversary of sorts, Jen turned the big 5-0 on Monday, prompting the actress to throw a star-studded bash (and reunite with ex-husband no. 1), and receive countless birthday tributes on social media (which the Friends alum doesn’t have, but I guess it’s the thought that counts?).

Among the barrage of Instagram birthday posts came one from the second of Aniston’s ex-husbands: Theroux.

The former couple has clarified throughout the past year that their split was amicable and they’re still friendly, a point the Leftovers star proved when he posted an adorable black-and-white photo of his ex goofing off (and flexin’ those inimitable Aniston arms).

“Happy Birthday to this fierce Woman,” Theroux’s caption began. “Fiercely loving. Fiercely kind. ….and fiercely funny. you B.”

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RELATED: Justin Theroux Finally Breaks His Silence on Divorce from Jennifer Aniston

So, so sweet. But before you sink into a puddle of mush, can we analyze that mysterious “B”? “B” as in … Baby? Beautiful? We need answers, Justin.

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