Andrew Walker on His ER Episode with Rachel Boston Ahead of Hallmark Reunion (Exclusive)

Some cycles are meant to be repeated. That certainly seems to be the case for Hallmark Channel favorites Andrew Walker and Rachel Boston.

The actors first appeared together in an episode of ER in January 2008. Years later, they costarred in Lifetime’s A Christmas in Tennessee. And, now, they’re back together yet again for Hallmark Channel’s Adventures in Love & Birding, premiering Saturday, Sept. 27.

“Rachel does everything with such an open heart,” Walker tells PEOPLE. “I like working with new people, but to have someone who I have this history with was an amazing opportunity.”

Looking back on his ER experience, Walker, 46, notes that the episode (called “Status Quo,” which aired during the hit NBC drama’s 14th season) was “extremely intense.”

“We played two military people, and she gets back from Afghanistan, and she’s pregnant, and it’s not our baby,” he recalls. “It’s an episode that talks about rape in the military. We had to go to a lot of different places emotionally.”

Walker says it was producer John Wells — who’s also worked on such other hits as Shameless, The West Wing and, most recently, The Pitt — who thought to pair him with Boston.

“He was the one that said, ‘Hey, you two, do a chemistry read together because I feel like there’s chemistry here.’ So, out of all the actors that had auditioned for that episode, he put us together and then ended up casting us in those roles,” Walker remembers.

Seventeen years later, Walker and Boston’s latest collaboration, Adventures in Love & Birding, is decidedly lighter fare.

“I am so grateful to be able to show the complex and beautiful story on ER, but I’m also so happy that [Adventures in Love & Birding] is a lighter, happier story,” Boston, 43, told EntertainmentNow. “We’re literally out in the woods, in nature, and it was just fantastic knowing [Walker] so well that we could just lean in from day one.”

The movie, inspired by Sarah T. Dubbs’ novel Birding with Benefits, follows a single mom (Boston) who agrees to be the partner of a bird enthusiast (Walker) for a birding competition but, due to a miscommunication with a mutual friend, thinks she’s supposed to pose as his new girlfriend instead of just his teammate. Needless to say, sparks, like the birds themselves, fly.

“It’s a beautiful love story and a very interesting one where we have this safety net of being able to explore with the understanding that we’re in a new relationship, when we’re really not, we’ve just really taken to each other,” says Walker. “It’s a beautiful movie about patience and understanding.”

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Adventures in Love & Birding premieres Saturday, Sept. 27 at 8 p.m. ET/PT on Hallmark Channel.