Slow Horses season 4 star Hugo Weaving teases his potential return as villain Frank Harkness in future seasons of the show

Warning: the following features spoilers for the Slow Horses season 4 finale.

Well, that was a jaw-dropping finale. Slow Horses season 4 ended with a bang as it was revealed that Hugo Weaving's mysterious villain Frank Harkness is actually the father of Jack Lowden's character River Cartwright, arguably the protagonist of the much beloved Apple TV Plus show.

And if that wasn't enough, the season ends with Frank being released by MI5 after being captured. If you have dirt on the secret service, you really can get away with anything.

As the menacing Frank tells Kristin Scott Thomas' Taverner, he's just getting started, leaving us wondering whether he will return for the upcoming Slow Horses season 5, which is already in the works. The door certainly has been left open for his return and Harkness is too much of a compelling bad guy to leave off our screens. As we noted in our Slow Horses season 4 review, Frank is the "show's best threat to date".

When we ask Weaving if he's returning as Frank, the actor tells GamesRadar+ that he "can't really talk about that", clearly wanting to shy away from spoilers for future seasons. However, he did tease that you can look to author Mick Herron's books for clues given that Slow Horses is an adaptation of his Slough House series.

As Weaving reveals, Harkness does appear in several books hinting that there will be more to come: "I can't really talk about that but suffice to say people who have read the books knows that Frank does return. At the end of the finale, Frank does kind of get away with everything and lives to see another day. So, you have to ask 'will we see him again?' Presumably we might."

Continuing, Weaving adds that he certainly hopes to reprise the role as he "really enjoyed playing him" and already has ideas for what he would like to explore further with the character. And as you probably guessed, it's Harkness' relationship with his estranged son River: "I would like to see how his relationship with River develops. Jack Lowden is a fabulous actor and he gives River a great humanity. It was a real pleasure working with him."

Slow Horses season 4 is available to stream now on Apple TV Plus. Check out our ranking of the best shows on Apple TV Plus. For more upcoming television that needs to be on your radar, here's our guide to the best new TV shows to watch out for.