*Warning - contains major spoilers for Slow Horses season 6 episode 6.*

The final episode of Slow Horses season 6 brought with it some huge moments, including the death of long-time character Emma Flyte and the departure once more of Louisa Guy.

However, in a surprise move, perhaps the biggest shock was left for last, as Jack Lowden's River returned to his grandfather's home to find Olivia Cooke's Sid staying there.

Wanting to surprise her, he entered the house as she was in the bathroom and started to prepare tea. He then changed his mind and pivoted to preparing a bottle of wine, but while doing so he grabbed a crowbar and put it away.

Immediately, he started looking at his hand, sensing something was wrong, but he continued for a time, until he collapsed to his knees, breathing heavily - apparently having been poisoned.

He tried to call out to Sid as he collapsed to the floor fully, but was unable to, as he gasped for breath. On that note, the episode ended off, leaving us with a whole lot of imminent questions, the most prominent being: Is River dead?

Speaking exclusively with Radio Times about this moment, Roddy Ho star Christopher Chung said he was "shocked" by it, and that he had already told people, without spoilers, that the scene would leave them "infuriated that you have to wait another year for the next one to see what happened".

"Jack was fantastic in that scene," he added, "but I think it is the biggest cliffhanger that this series has ever done before, so I'm interested to see how that lands."

Director Adam Randall also unpacked how he brought that scene to life while speaking with , noting that the stillness and quietness of it was very intentional.

"I really wanted for you to know something was wrong, because we were taking so long with absolutely nothing happening," he said. "It's almost the most wonderful happy ending. It's sort of heartbreaking that it isn't.

"I just remember going in there on my own and sort of thinking about, ‘What would you do?’ You get the tea, and then you maybe feel a bit embarrassed that you're making tea. You really fancy her, 'What are you making tea for? She's up there, go get the wine out.'

"And so I sort of did a little walk around on my own in that kitchen, and then Jack came in, and we talked it through, and then he throws ideas in, and we just tried to stretch it out as long as possible."

Randall continued: "Then I really wanted to use this Nick Drake song because it was a little callback. We used Nick Drake at the end of season 4, but also it's got this lovely quality, that track, where there's a sort of sweetness and it's kind of upbeat, but it's really melancholic.

"And the way to use that music where it's sort of diegetic, and then it's not, and to be as subtle as we could with what was happening with his hand. How little can we get away with before…

"And what's so interesting about that is it's a very dark season, lots of things go wrong for various people. So you're not expecting for it then to be the darkest and then it just ends. It's shocking and it's a risk, really. But it is in the book, and it's important. It's an important part of the story."

Thankfully, we do know that even if River himself doesn't return, Slow Horses certainly will. A seventh and eighth season have both been commissioned, and a trailer at the end of episode 6 has already given us a hint towards what we can expect in the former.

In the trailer, Catherine Standish is seen asking Jackson Lamb exactly what we all want to know: "Have you heard something? about River?"

Lamb responds ominously: "Yeah, funny enough I got a postcard. Weather's lovely in the afterlife. Sunsets to die for. Love and hugs."

Sadly, we can't say we're reassured.

Add Slow Horses to your watchlist on the Radio Times: What to Watch app – download now for daily TV recommendations, features and more.

Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on. For more TV recommendations and reviews, listen to The Radio Times Podcast.