Outlander's Sam Heughan reveals he's forced to keep this secret from co-star Caitríona Balfe

Outlander star Sam Heughan has revealed the one secret that he's been forced to keep from his co-star Caitríona Balfe - and it's how the show ends!

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In a recent interview with Esquire, the 42-year-old said that Diana Gabaldon, who writes the novels upon which the show is based, has told him what will happen at the end of the entire series.

WATCH: What did you think of season six? 

"Diana Gabaldon actually revealed to me how the whole thing's going to end," he said. "She emailed me the last few pages of what will be the last book very early on, I think in the first few weeks of shooting and no one else has seen that I think, apart from one other exec producer.

"Even Caitríona’s not seen it and I'm sworn to secrecy," he added.

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At the end of season six, fans watched in shock as Claire and Jamie were ripped apart, with the former being whisked away in a wagon on her way to jail while the latter was tied up by Brown's men awaiting a boat to Scotland.

Sam knows how the entire series will end

Luckily, Young Ian came to Jamie's rescue just in time and the episode ended with the duo, along with Myers and some others, riding across the beach, presumably on the way to save Claire.

In the same interview with Esquire, Sam also gave a devastating update about the upcoming prequel series, which is set to tell the love story of Jamie's parents, Ellen and Brian Fraser.

"All I can tell you is I'm not in it, as Jamie's not in it!" he revealed.

Sam gave a sad update about the prequel series

"I believe that it's a prequel focusing on Jamie's parents when they were younger, so I guess you might see a young version of him at some point. But I think I may be a little too old to play young Jamie now! I could play his dad maybe, or a flash forward? It is time travel, after all."

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