From the beginning, it was evident that the success of Outlander's TV adaptation relied heavily on the chemistry between its two stars. Fans of the series had already fallen in love with Claire and Jamie's love story through Diana Gabaldon's books, and they demanded nothing short of a believable portrayal of their passion and loyalty.

Casting the leads became a careful and lengthy process. Sam Heughan, a relatively unknown actor at the time, was chosen to play the rugged 17th-century Scot, Jamie Fraser.

"This was a vital step before casting Caitriona because we had already cast Sam," explains the original showrunner Ronald D. Moore in a clip featured in the Outlander season three Collector's Edition Blu-ray. "We were looking for chemistry between the two characters. We already felt that Cait was the one, but this was the moment that sealed the deal. As you can see, they already had the shorthand of their characters and there was definitely on-camera chemistry between them."

The video showcases an emotional scene performed by the pair, but what spoke volumes was how they continued to interact even after all the lines were delivered.

"After the scene finished, we let the tape keep rolling a bit longer to see them relaxed and interacting," Moore reveals. "The spontaneity, genuine affection, and good humor between them revealed their potential relationship."