Over a decade after landing the leading heroine role in the beloved time-travel series “Outlander,” Caitriona Balfe remembers that the first time she was set to meet Sam Heughan, who would become her on-screen husband for the eight-season run of the Starz show, she was stuck in L.A. traffic.

“There was roadwork or something, and I was kind of running late, and I walk into the room, and [Sam] was just such a kind, calm center, and he handed me a tissue because I was all sweaty,” Balfe told TheWrap. But none of that mattered once she and Heughan started reading as Jamie and Claire.

“It just was instantaneous,” Balfe added. “We got into the scenes and we had such a good chemistry together, and it was, I don’t know, there was just a natural flow between us.”

It was that same flow that Heughan, who was cast before Balfe, recalled from their chemistry read, which was welcome after he and the team had auditioned a number of actresses for the role of Claire. “There was a real struggle to find the actress to play her, and I got to do chemistry reads in the U.K. and in the U.S. with a number of really talented people.”

“But I think when Caitriona walked in, it just had a different energy to it,” he said. “It was very passionate and very charged. I think the moment she came in, everyone knew.”

It was merely a week later that Balfe was on a plane to Scotland with two scripts in hand, full of nerves and excitement. “I just didn’t know what to do with myself — I was sitting on the plane trying to read these scripts, just like, ‘I can’t believe what’s happening. I don’t know what I’m doing,’” Balfe said. “I’d never done TV before. I hadn’t ever even been on a TV set, so I was incredibly nervous.”

Once she landed in Scotland, Balfe hit the ground running into fittings and horseback riding lessons — “because, of course, I’d said I could horse ride and I couldn’t,” she said — likening adapting to becoming a series star to Claire’s unfamiliar territory as she time traveled from 1945 to 1743 for the first time.

“My experience of being thrown in at the deep end sort of mirrored Claire’s experience. It was really good in that way, because it helped me get through it,” Balfe said, “But it was so magical. I also remember the first two weeks of filming, the weather in Scotland was so beautiful, and I would just see rainbows nearly every day.”

Heughan, on the other hand, felt a deep connection to Jamie even prior to the audition as he read the “Outlander” books, recalling, “I just felt like I knew this character. He felt quite familiar to me.”

While Claire’s brilliance and capability from the book shines through as she adapted to her new whereabouts, Balfe wanted to ground her in some realism during Season 1, which alone sees her ripped away from her husband and daughter, leaving her with nothing as she attempts to find her footing in a new time period.

“I remember talking to the writers and I was like, ‘She can’t just go through situations and it not affect her at all — we have to allow some of these things to land,’” Balfe said. “It is that thing of you want strength, but you also want vulnerability and finding the balance of that. That was what I was always interested in.”

It’s for that reason that Balfe admitted she liked that Claire was able to fall apart and heal again by Season 6, in the aftermath of her capture and assault. “I think that’s a really important thing that we get to show people that nobody’s Superwoman or Superman — you will have dark days, and there will be times when you can’t always face the world, but actually, if you allow yourself to get through that, you will come out stronger in the end,” Balfe said. “Claire emerged from all of that as somebody who’s much more human and much more resilient, because she’s allowed that fragility to show.”

While Claire had already been a wife and mother by the time she met Jamie, Heughan got to see Jamie grow up throughout the years, from a “rather tempestuous independent warrior, fighting his own battles, to then having something to fight for, to being responsible, being a father, a clan leader, in some ways, a leader of men, a general.”

“His decisions [have] more consequences than just on him and his family, but also over time, knowing that what they do now would have repercussions in the future,” Heughan said. “Where we find him now in Season 8 is that he is older, but he’s also perhaps more fragile and more aware of what he has to lose.”

Through it all, Jamie and Claire have always found their way back to one another, with Balfe joking, “they’ve been through some stuff, haven’t they?” and pointing to Season 7 finding Claire having to marry somebody else entirely for a spell.

“It’s so beautiful to watch an enduring love and two people fight for each other — they’ve both gone through the really tough times, and it’s not always plain sailing, but that’s what a real marriage is,” Balfe said. “You stick together, and … you let the tough times exist, and then you try and get past it, and you allow the other person to have their moments of maybe not wanting everything, but … the fact that they’ve endured this long is the beauty of it.”

As Balfe and Heughan prepared to say goodbye to Jamie and Claire in the eighth and final season of “Outlander,” they admitted it was a tough installment to film, with Balfe noting “you have so many expectations, and it’s been so long, and everyone wants to do the best” came hand-in-hand with “saying goodbye to different locations and different people and knowing it’s the last time.”

“Most days you were saying goodbye, in some ways, whether it was the last time you were on set in a certain location or with a particular actor or character, you could feel a sense that this was coming to an end, and that was hard,” Heughan said. “But then other times, you realize it just felt like another day on set, so it was a bit of a rollercoaster.”

“The last day was probably the most emotional I’ve been in such a long time,” Balfe added. “It was a scene with Sam and I, and we were both, by the end of it, just sobbing, and we had everybody there. All of the cast had come to the studio and all of the producers and all of our execs, and it was really special. It was so emotional for everybody.”

At the time of the interview ahead of the final season, both stars said they didn’t actually know how “Outlander” will wrap up in the series finale, with Balfe noting showrunner Matthew B. Roberts filmed multiple endings that he would decide on later. “It must be so impossible when you’re finishing a season or finishing a show and writing it, showrunning it, everyone wants to give you their opinion, and everyone has an idea, so he kept his cards very close to his chest,” Balfe said.

“I don’t know how it ends, particularly, I haven’t seen it,” Heughan said. “We had multiple things we shot. I certainly think I know how it ends, and I hope the fans enjoy it. But yeah, it’s going to be it’s hard to end a show like this, and I’m sure for most people, it’ll be bittersweet.”

Of course, fans will have spinoff series “Outlander: Blood of my Blood” to grasp onto after the flagship series ends, but it’ll likely be the last time they see Balfe and Heughan on-screen due to the prequel’s nature. “Unless I’m playing a younger version of myself, and I don’t think that’s going to happen, but you never know, maybe they could write me a cool part,” Heughan said.

As the leads move on to their next endeavors, they’ll both indelibly be touched by show’s legacy, with Balfe noting Claire has “changed [her] life in so many ways.”

“Just the sort of capacity that she had for everything — for love, for rage, for empathy, for caring … I think that that has stretched me in so many ways, and I will bring all of that with me into everything I do going forward,” Balfe said. “She’s going to live with me forever. I don’t think you play a character like her for as long as I did, and not take them with you.”

“Outlander” Season 8 releases new episodes Fridays on the Starz app, and Sundays on Starz’s linear channel.