And his reply has fans losing their minds!
Or so he jokingly proclaimed. It's hard to tell when there were close to 200,000 replies left on the actress' debut post in the first four hours of its existence.
But perhaps more telling than even the act of leaving a comment are the contents of said comment.
"Woot-Woot! #first," Theroux wrote, along with a hands-up (praise) emoji and a heart. Yes! A heart.
Aniston's first photo on the app -- a selfie alongside her "Friends" co-stars and the caption, "And now we're Instagram FRIENDS too. HI INSTAGRAM" -- elicited such joy and excitement among her famous and non-famous friends and fans that several people reported having issues following her!
Among those welcoming the "Horrible Bosses," "We're the Millers" and "Bruce Almighty" star to the social media network were Reese Witherspoon ("YASSSS!!! Welcome to Insta Jen!!!"), Courteney Cox ("love you"), Chelsea Handler ("Oh, yeah tushy!"), Jenna Dewan ("Yessssss!"), Whitney Cummings ("All I can say is MUTE BUTTON"), Olivia Wilde ("FINALLY"), Kerry Washington ("WELCOME TO THE GRAM!!!!"), Kyle Richards (three sets of clapping-hand emojis), Kaley Cuoco ("I. Can't. Handle. This."), Ashley Tisdale ("EPIC"), Lala Kent ("I die I die I die"), Colton Underwood ("History."), Erin Foster ("This is big") and Sara Foster ("I guess you didn't go with the nude like I suggested, but this pic is cute too. So happy you are here!!!!!!!").
Even Comments By Celebs ("What a day to be alive") and Instagram ("Welcome!!") were stoked.
Theroux married Aniston in 2015; they were divorced two years later. The actress' previous marriage was to Brad Pitt, from 2000 to 2005.
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