With 'The Big Bang Theory' coming to an end, let's take a look back at one of the most enduring relationships on and off screen.
With The Big Bang Theory coming to an end on May 16, let's take a look back at one of the most enduring on-screen and off-screen relationships that blossomed from the long-running show -- that between Kaley Cuoco and Johnny Galecki.
Cuoco, 33, and Galecki, 44, play Penny and Leonard, respectively, on the hit CBS show, who ended up getting married in season nine. In real-life, Cuoco and Galecki actually secretly dated from 2007-2009. Cuoco dropped the bombshell in a 2010 interview with CBS Watch! magazine.
"It was such a huge part of my life and no one knew about it," she said. "It was a wonderful relationship but we never spoke a word about it and never went anywhere together. We were so protective of ourselves and the show and didn't want anything to ruin that. ... We knew how to keep it deep inside and never bring it on that set, ever."
"That's not the kind of relationship I want," she admitted, looking back. "I don't want to be hiding. We couldn't do anything. It wasn't as fun as we wanted it to be. Everyone was always asking, and we deny-deny-denied. And I'm like, 'Why am I denying this person that I love?' It took a little bit of a toll on me and I think it did for him, too."
She also stressed that the two always planned to never let their personal relationship interfere with their work.
"Moments were really hard, but we have such a love for each other -- and we knew we weren't destined to be together -- that we accepted it and said, 'Look, if we ever break up, we will be professional,'" she said.
In 2013, Galecki had his own interview with CBS! Watch magazine, and talked about the two still being close.
"We're dear friends, still," he said. "Kaley's not just an ex, she's a part of my life."
"I just don't like to speak about it," he added of their secret romance. "And not because I'm trying to be enigmatic; I just worry that it will conflict with people's acceptance of [Big Bang Theory characters] Leonard and Penny. I get the curiosity, but I don't want to distract from the story."
In September 2015, Cuoco echoed that there was zero awkwardness between the exes during her appearance on Watch What Happens Live With Andy Cohen -- so much so that her now ex-husband, former tennis pro Ryan Sweeting, was a fan of Galecki's.
"Well, we dated, like, five years ago, so I think we both moved on," Cuoco noted of her co-star. "Johnny is actually one of my best friends. It’s a situation that ended well. I understand sometimes it doesn’t. It could have gone horrible."
"He's one of my dearest friends and Ryan loves him," she added. "Johnny loves [Ryan]. I got lucky."
Obviously, Cuoco and Galecki still have a lot of love for one another following their split and have even sparked dating rumors since. In October 2015, after Cuoco filed for divorce from Sweeting, she Instagrammed a photo with Galecki and made it clear they weren't back together now that she was single again.
"So sorry to disappoint, but no home wreckers or secret flings going on here," Cuoco wrote. "Me and @sanctionedjohnnygalecki are just the best of buds -- Leonard and Penny will just have to suffice!"
At the People's Choice Awards in 2016, Cuoco and Galecki showed plenty of PDA, and Cuoco once again shot down dating rumors.
"Thank you for the @peopleschoice award!! Look how happy we are!! @bigbangtheory_cbs season9," she Instagrammed alongside a collage of the two with the hashtags "#mydate" and "#notdating."
The two have also been more comfortable discussing their past romance in a lighthearted way. During their Comic-Con appearance in 2017, Big Bang Theory executive producer Steve Molaro shared a story of the first Comic-Con panel for the show in 2007, where he unknowingly crashed a fight between Cuoco and Galecki at a hotel bar, when they were secretly dating at the time. Though the exes and co-stars couldn't recall exactly what they were fighting about, Cuoco shared that she was about ready to cry and urged Molaro to stay at the bar.
"I think it was a great bonding moment for me," Cuoco joked, adding that she’s since gone to Molaro for relationship advice.
Of course, it helps that Cuoco and Galecki have both moved on romantically. Cuoco married equestrian Karl Cook last July, and Galecki attended the wedding and later shared a touching post marking the occasion. Galecki sweetly called Cuoco his "fake wife."
"Couldn’t be happier for my fake wife @normancookand @mrtankcook whose words brought us all to tears last night," Galecki captioned a sweet black-and-white pic of him and Cuoco clasping hands and sharing smiles on her big day. "So much love for you both."
The actor also posted a photo with both Cuoco and Cook, writing, "Deepest congrats to the newlyweds. Love you both so much @normancook & @mrtankcook So moved by tonight."
Earlier this month, Galecki announced he and his girlfriend, Alaina Meyer, are expecting their first child together, after going public with their relationship last September.
"We are absolutely over the moon to announce that we will soon be welcoming a little one into this crazy and wonderful world," Galecki Instagrammed. "We ask that you please respect our privacy during this celebratory time for us and our families. There truly is love out there for all. We hope ours is the ember of yours, as we feel yours is the ember of ours."
These days, as fans await the bittersweet ending of The Big Bang Theory after 12 seasons, it's clear the end is also hard for both Galecki and Cuoco. The two said they had a shared vision for the finale of the show in an interview with Entertainment Weekly in January -- finally fixing the broken elevator.
"None of us are going to be able to keep from crying during the last taping," Galecki added on a more serious note. "We've got to justify it in the writing somehow, sensitive group."
ET spoke with Cuoco at the Golden Globes in January, when she also talked about the emotional ending of The Big Bang Theory.
"I was laughing. I was like, 'How are we gonna shoot the last episode?'" she recalled. "I was hoping we were gonna pre-shoot a lot of it 'cause I think there are gonna be a lot of tears."
"It’s gonna be tough, it’s gonna be a lot of emotions and I love our crew," she continued. "I just love the people that we’re with every day so, you know, all good things come to an end. Everyone is still madly in love with each other. We're all OK with the choice. We’ve just grown up together, so it’s our adult decision."
Indeed, Cuoco already burst into tears during the last table read for the show last month. The actress Instagrammed a shot of herself in full-blown tears, writing, "Post table read for @bigbangtheory_cbs finale episode."
ET actually spoke with both Cuoco and Galecki in March, when their chemistry and playful nature was still on full display. The two weren't afraid to poke fun at one another, and Galecki joked he didn't even know Cuoco had green eyes after 12 years of working together. He did, however, call them "beautiful."
Watch the video below to see their adorable exchange:
'Big Bang Theory' Cast Shares Their Favorite Moments as They Say Goodbye to Iconic Series (Exclusive)
Kaley Cuoco Says She's 'Thrilled' With Where Penny Ends Up in 'The Big Bang Theory' Series Finale (Exclusive)