Justin Theroux Explains Why He Initially Wasn't Following Jennifer Aniston on Instagram (Exclusive)

The actor tells ET that Aniston called him out after she noticed he wasn't following her.

Justin Theroux was caught in the glitch! 

The 48-year-old actor was among the first stars to follow Jennifer Aniston when she joined Instagram last week, but as he told ET, his follow didn't register -- and his ex-wife called him out for it. 

"She actually texted me. She said, 'You haven't followed me,' and I said, 'Of course I followed you!' and she's like, 'No you haven't!'" Theroux told ET's Rachel Smith at the New York City press day for Lady and the Tramp on Wednesday. "I realized I was one of the people caught in the glitch. So, I had followed, commented..." 

"Wait a minute, was there an actual -- she created an A-listed glitch?" Theroux's co-star, Tessa Thompson, asked. 

"Like, literally broke Instagram. People were having trouble being recognized as following," he shared. 

"Well, it's good that I waited till past the glitch. I'll just be like, 'Jen, notice me!'" Thompson replied. 

Aniston has already mastered social media with her first selfie, #TBT and more. As for Theroux's own Instagram habits, he usually goes for a good dog pic. His pup, Kuma, is not only a social media star but a movie star as well; she appears in Lady and the Tramp. 

"It went fine," Theroux said of Kuma meeting Monte, who plays Tramp in the movie. (Theroux voices the character, while Thompson voices Lady, played by Rose.) "[Monte is] so well trained that [Kuma's] just like, 'Ah... just wanna talk to you. You're the tramp.'" 

"Was she starstruck?" Thompson asked. 

"100,000 percent, even though she's in the movie too -- not to brag," he noted. 

As for Theroux and Thompson's first meeting, that happened in London before they started work on Lady and the Tramp -- but they really got to know each other in the studio. 

"We actually met in London previously and hung out together and it was sort of one of those happy accidents where we were like, 'Oh my god, we're gonna be working together!' So, we had the good fortune of having some good social time together and then this," Theroux said. 

"And the cool thing is that we were always in the studio together, which sometimes is rare. Sometimes when you get these performances, people are in different countries or don't have the opportunity to meet, but we were together, which meant we got to do lots of improv and figure out scenes sort of while we were going and come to know each other," Thompson added. 

Lady and the Tramp is available to stream on Disney+ starting Nov. 12. See more on the movie in the video below.