Andrew Walker and Rachel Boston’s on-screen history has spanned some serious highs and lows — from the weighty drama of ER to the cozy comfort of Hallmark.

The pair first worked together in a Season 14 episode of the NBC medical drama back in 2008, before reconnecting years later for Lifetime’s A Christmas in Tennessee. Now, they’re joining forces again in Hallmark’s Adventures in Love & Birding, which premiered Saturday, September 27 at 8 p.m. ET/PT.

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

That history began with a particularly heavy storyline. “We played two military people, and she gets back from Afghanistan, and she’s pregnant, and it’s not our baby,” Walker recalled of their ER roles. “It’s an episode that talks about rape in the military. We had to go to a lot of different places emotionally.”

Walker credits producer John Wells (The West Wing, Shameless) for pairing them back then: “He was the one that said, ‘Hey, you two, do a chemistry read together because I feel like there’s chemistry here.’”

Seventeen years later, the tone is much lighter. Adventures in Love & Birding — inspired by Sarah T. Dubbs’ novel Birding with Benefits — casts Boston as a single mom who partners up with Walker’s birding enthusiast for a competition. Thanks to a misunderstanding, she thinks she’s supposed to pose as his girlfriend instead of just his teammate, and yes, romance soon takes flight.

“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 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.”

Walker sums it up: “It’s a beautiful movie about patience and understanding.”

Hallmark’s Adventures in Love & Birding premiered Saturday night.