The actor, 31, shared a video of the emotional moment on Instagram on Sunday, Feb. 16. In the footage -- which was shot a few weeks after his 2023 engagement to fiancée Abby Champion -- he spills the casting news to his mom, Maria Shriver, and his sister Katherine Schwarzenegger.
"At first, I was told I had to keep it a secret, but my family kept noticing me acting weird," he wrote on Instagram. "Maria thought Abby and I were pregnant đ€Ł. She might have been happier than I was!! And then I started crying. She did. Katherine did. Was a domino effect. Mind you this was in a restaurant with other people lol."
Patrick previously told PEOPLE for February's digital cover that finding out he secured a main cast role on the hit HBO anthology series "was the greatest day in history for me" -- but he had to keep it secret.
Related: Jason Isaacs Admits Why He 'Lied' to White Lotus Creator Mike White During His Season 3 Audition (Exclusive)
"Obviously I'm going to tell my fiancée because we got engaged the week before, and I was like, 'Sorry, I'm leaving for seven months [to film in Thailand].' So that was perfect timing," he told PEOPLE with a laugh. "Then I went and had lunch with my whole family the week later, and I told them."
Patrick also recalled watching the first two seasons of The White Lotus with his family and how they nudged him to audition for the third season, which premieres on Sunday, Feb. 16.
"Every time we would watch the show ... my mom was always like, 'Why haven't you auditioned for this? Why didn't you go out for this?' And my sister's like, 'You need to call your agents right now. This is ridiculous that you're not in on the show, that you didn't even audition,' " he added.
Related: Arnold Schwarzenegger's 5 Kids: All About His Sons and Daughters
He later received an email to audition, but "didn't tell anybody because I was like, 'Whatever, everyone's going to go out for this show. I have such a sliver of a chance to get a call back,' " he remembered thinking.
In season 3, Patrick plays Saxon Ratliff, the eldest son of Timothy (played by Jason Isaacs) and Victoria (ParÂker Posey), who works for his father's company. Along with Saxon's siblings (Sarah Catherine Hook and Sam Nivola), the family of five are among the guests vacationing at a resort in Thailand who experience trouble in paradise.
Patrick told PEOPLE that Saxon is a "complete flirt" and an "alpha male."
Related: Who's Playing Who in The White Lotus Season 3? A Guide to the Star-Studded Cast Headed to Thailand -- and the Eccentric Set of Characters They Portray
The cast and Patrick's family, including famous father Arnold Schwarzenegger, celebrated the new season at the Los Angeles premiere at Paramount Theatre on Feb. 10.
After the event, Arnold posted an Instagram photo of the family together on the red carpet and poked fun at his son's nude scene in the show.
"What a show! I could claim to be surprised to find out he has a nude scene, but what can I say -- the apple doesn't fall far from the tree," Arnold, 77, wrote in the caption. "Don't miss it this Sunday -- trust me."
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This season's main cast also includes Leslie Bibb, Carrie Coon, Walton Goggins, Lalisa Manobal, Michelle Monaghan, Lek Patravadi, Natasha Rothwell, Tayme Thapthimthong and Aimee Lou Wood.