The actress starred on the beloved CBS sitcom for 12 seasons.
The Ozark alum shares a funny story about a big milestone in their relationship, revealing that Cuoco was a great sport when it came to a mix-up with her name.
"When I first brought Kaley to New Jersey to meet my family and friends, my mom's partner -- who apparently was a Big Bang Theory fan -- was there, and he kept calling her Penny," Pelphrey says in an interview for W Magazine's fourth annual TV Portfolio. "I had no clue what was going on. So I pulled Kaley aside, like, 'I'm sorry, I don't understand what's happening. Why does he keep calling you Penny?' She's like, 'That's my character in The Big Bang Theory.'"
As it turned out, Pelphrey had not yet seen Cuoco's performance as the beloved leading lady in CBS' long-running sitcom.
"I was completely unaware," he admits. "I've watched a few episodes with her since, and, obviously, she's fantastic."
Cuoco starred as Penny in the Chuck Lorre-led show for 12 seasons, premiering in 2007 and wrapping in 2019. The Big Bang Theory also starred Cuoco's ex, Johnny Galecki, as well as Jim Parsons, Simon Helberg, Kunal Nayyar, Melissa Rauch and Mayim Bialik.
Pelphrey is featured in W Magazine for his role opposite Elizabeth Olsen in HBO's Love & Death. He's in good company with some of the year's biggest small screen standouts, including Meghann Fahey (The White Lotus), Matthew Macfadyen (Succession), Sheryl Lee Ralph (Abbott Elementary), Dominique Fishback (Swarm), Camila Morrone (Daisy Jones & The Six), Keri Russell (The Diplomat), Young Mazino (Beef), Salma Hayek (Black Mirror), Kerry Washington (UnPrisoned), Cara Delevingne (Only Murders in the Building, American Horror Story) and Elle Fanning (The Great).
In Love & Death, based on the true story of Candy Montgomery, Pelphrey plays Don Crowder -- the inexperienced lawyer who defends Olsen's Montgomery.
"I'm somewhat of a true-crime fan," Pelphrey says, noting that Cuoco "loves Dateline."
He continues, "So sometimes I'm absorbing it just by proximity. The Candy Montgomery story is pretty fascinating because it's one of those stories where truth is stranger than fiction."
Cuoco also took a stab at the true-crime genre this year with Peacock's Based on a True Story.
Pelphrey, 41, and Cuoco, 37, share the same manager and met in April 2022 at the Ozark premiere.
"I went inside, I was so excited," Cuoco previously told ET of their meet-cute, "and we met there -- and it was love at first sight."
Less than a year later -- on March 30, 2023 -- the couple welcomed their first child, daughter Matilda Carmine Richie Pelphrey.
"We got pregnant two months in," Cuoco said on the Smartless podcast in June. "We're like, boom, boom, boom. We're in sync."
The whirlwind nature of their romance was a welcome change of pace for the duo.
"We're not 20 anymore," Cuoco admitted. "We were like, 'We doing this or not?'"
Speaking with ET at the June premiere of Based on a True Story, Cuoco gushed over Pelphrey's enthusiastic support of her work.
"I wish he was here, you know, he loves this show. I don't know if he's biased 'cause he, like, really likes me, but we watched all the episodes and he was like, 'Are there more?' He wanted more," she said. "He's like, 'It's so much fun.' So he loved it. That always makes you feel good when your partner is like, 'Yes, yes, yes!'"