Justin Theroux and Jennifer Aniston may have broken up, but they have no hard feelings for each other.

On Monday, Theroux made sure to wish his ex-wife a happy birthday when she turned 50 years old on Feb. 11. The "Leftovers" star took to Instagram to share black and white photo of Aniston who can be seen holding up what appears to be horns. In the snap, the "Friends" star had a fierce expression as she posed in a black tank top. 

Theroux also wrote a simple but sweet message for Aniston, whom he was married to for two years before they announced their separation last year. "Happy Birthday to this fierce Woman," he said. "Fiercely loving. Fiercely kind. ....and fiercely funny."

He ended his message by saying that he loves her. 

Theroux's post has since received over 100,000 likes and thousands of messages from his followers. 

In September last year, Theroux opened up about his split from Aniston during an interview with The New York Times. He revealed that they remain "amicable" with each other, contrary to rumors claiming that the many speculations about them claimed.

But while their split was a mutual decision, it was still "heartbreaking," according to the actor, especially since it affected their friendship. The two had been in a relationship before they decided to part ways in 2017. 

“The friendship would not be the same, as far as just the day to day. But the friendship is shifting and changing, you know, so that part is something that we’re both very proud of," Theroux told the publication. 

Meanwhile, despite wishing his ex-wife a happy birthday, Theroux wasn't among the celebrity guests at Aniston's lavish bash over the weekend. However, two of Aniston's exes did make it, Brad Pitt and John Mayer.

Pitt's appearance was especially shocking as most were unaware that the two maintained a friendly relationship with each other after their split. 

A source recently told Entertainment Tonight that Pitt decided to come and celebrate with Aniston at the Sunset Tower hotel because he wanted to show his support for her. 

“He came to support her, spoke to other friends of his that were there and headed out,” the insider said.

However, Pitt reportedly didn't stay the entire night. He did share a hug with Aniston and chatted with her for a bit, before hanging out with George Clooney and Orlando Bloom.  

Aside from Pitt, many of Aniston's celebrity pals also attended her 50th birthday party, including Clooney's wife Amal Clooney, Reese Witherspoon, Courteney Cox, Lisa Kudrow, Robert Downey Jr., Ellen DeGeneres, Barbra Streisand, Keith Richards, Kate Hudson, Laura Dern, Demi Moore and Jennifer Meyer, People reported.

Justin Theroux, Jennifer Aniston Justin Theroux wished his ex-wife Jennifer Aniston a happy birthday on Monday. Pictured: Justin Theroux (L) and his wife US actress Jennifer Aniston (R) pose during a photocall ahead of a diner for the launch of a Louis Vuitton leather goods collection in collaboration with US artist Jeff Koons, at the Louvre in Paris on April 11, 2017. Photo: Getty Images/Gabriel Bouys