Jason Ritter on that ‘Matlock’ twist: ‘I couldn’t believe what was happening’

He’s on the case.

Jason Ritter co-stars in CBS’s hit legal drama “Matlock,” which follows Madeline “Matty” Matlock (Kathy Bates), a seemingly widowed and inexperienced ex-lawyer who takes a job at the law firm Jacobson & Moore. The show is a gender-bent reboot of the original “Matlock” starring Andy Griffith, which aired from 1986 to 1995.

“Matlock” aired its first episode as a sneak peek in September, snaring over 10 million viewers. The show’s regular time slot premiere is Thursday, Oct. 17 ( 9 p.m. on CBS).

“I couldn’t be more excited,” Ritter, 44, told The Post, referring to the show’s initial success.

Ritter, who is married to “Yellowjackets” star Melanie Lynskey and shares a 5-year-old daughter with her, added, “It sort of reminded me of dropping my daughter off to kindergarten. You’re like, ‘well, I think she’s awesome, but I hope the other kids like her!’ It’s a similar feeling, where you go from being in your little bubble out into the world. So, it’s been so exciting to see that other people have loved [‘Matlock’] as much as we do.”

As the first episode revealed – spoiler alert – there’s a twist.

Madeline is pretending to be a sweet older lady who needs the job for the money. But really, she wants to work at the law firm because she believes that Julian (Ritter), his soon-to-be ex-wife, Olympia (Skye P. Marshall), or his father, Senior (Beau Bridges), hid documents that indirectly relate to her daughter’s death and she wants to expose the culprit.

“When I auditioned for it, I didn’t realize about the twist until after I had gotten the part and I read the script,” said Ritter.

“I don’t think I’ve ever stood up while I was reading a script. I was sitting in a chair in the dining room and I couldn’t believe what was happening, I got so excited, I stood up…I had that same feeling of hearing that final click at the top of a roller coaster, going, ‘oh boy!’”

He added, “It’s also fun because the three people who are her main suspects all are very important to each other, it’s not like 3 strangers. They’re members of the same family.”

Ritter, who is the son of actress Nancy Morgan and the late John Ritter, said that he relates to Julian, in part, because the character also works in the same industry as his father.

“There was a lot of Julian’s character that I didn’t have to reach too far for. Aside from he has a very contentious relationship with his father, and I loved my dad,” said Ritter.

John Ritter passed away in 2003 at age 54 of thoracic aortic dissection.

Jason added that he “understood” Julian’s worries about what his colleagues think of him.

“Imposter syndrome… I’m very familiar with.”

He added that he most related to Julian’s “family stuff.”

“He obviously wants to be a good lawyer, he wants to make money and all of those things, but at the  very top of his list is he wants to be a good dad.”

Ritter said the hardest part of the role was not going fanboy on Bates.

“The biggest challenge for me was trying to stop myself from getting in my head and stopping myself from going, ‘This is so surreal, I can’t believe I’m talking to Kathy Bates!’ I have loved her so many years and have been in awe of so many performances.”

Ritter shared that he had to focus on “staying present in the scene and not floating out of my body and going, ‘This is so cool! She’s so wonderful!’”

As “Matlock” continues unfolding, Ritter said there will be many revelations and plot twists.

“This is a firm where there are a lot of secrets. It’s really fun to peel it all back layer by layer and see what disgusting things are underneath.”