“Outlander” star Sam Heughan is known for his fitness routine, but it’s his co-star Caitriona Balfe who is running the London Marathon Sunday. It’s the Claire actress’ first big race, and Heughan had to cheer her on.

“GO @caitrionambalfe !!!!! Eddie and I watching, with our feet up,” Heughan tweeted Sunday morning. He was watching the marathon on his tablet with a cat in his lap. He also wished everyone running good luck.

Balfe announced in February that she was training for the April 22 marathon with her sister Anne-Marie. The two raised money for one of Balfe’s favorite charities, World Child Cancer. They received over £28,800 (over $40,000) from “Outlander” fans, far more than their initial £6,000 goal.

Balfe and her sister attended the London Marathon Expo Saturday to speak about their decision to run. (Watch their chat on Facebook.) “I didn’t know if I’d be able to run this year, so I asked Anne-Marie to run on my behalf, but then she was like, ‘Well if I’m going to run, you have to run,’” Balfe said.

Caitriona Balfe Sam Heughan Caitriona Balfe had Sam Heughan’s support ahead of the London Marathon. They are pictured above at an “Outlander” event on March 18, 2018 in Hollywood, California. Photo: Amanda Edwards/Getty Images

The actress did a 10k run five years ago, so she isn’t an experienced marathon runner. However, she’s been balancing filming “Outlander” with training for a couple months. “I’ve actually discovered parts of Glasgow that I think I would never have known before, so that’s nice,” she said.

While her “Outlander” family supports her, they aren’t giving her a day off. The former model will have to head back to Scotland tonight to continue filming Season 4 tomorrow. “I’ve got about three hours to get nicely drunk and then pick up my suitcase and somehow make it back to the airport,” she explained.

She is hoping that her work will at least be easy on her sore muscles. “I’ve told them I’m only doing seated scenes,” she quipped.

Claire isn’t usually one to stay sitting for very long. Though executive producer Ronald D. Moore said this season was about Jamie and Claire “settling down,” executive producer Toni Graphia assured fans that the excitement isn’t over.

“[They] thrive, yeah, and [put down] roots, and face the challenges together because there’s a lot of challenges,” she told Parade. “Settling implies a boring thing, but it’s more like facing one obstacle after another and the challenges.”

“Outlander” Season 4 is expected to premiere on Starz later this year.