The first episode of EastEnders spin-off Kat and Alfie: Redwater has ended with a dramatic cliffhanger, thanks to Kat's long-lost son having been revealed to be a killer.

The BBC1 drama solved its central mystery in its opening hour as Father Dermott Dolan (Oisin Stack) was shown bumping off fellow villager Lance Byrne (Ian McElhinney).

Dermott had just been told by Lance that he was Kat's biological son, only for the priest to then lash out and drown the respected Redwater resident.

Speaking about the shock showdown, actor Oisin Stack said: "It's always nice when there's a real surprise and people aren't expecting what they're going to see."

Details of the identity of Kat's son had been kept back from viewers prior to transmission - and fans have yet to see whether Kat herself will find out who her offspring really is.

"What he [Dermott] did was a spur of the moment thing," Stack added to RTE, who showed the episode on Sunday. "There's going to be a lot of him trying to figure out exactly what happened and what the truth is. Because he himself doesn't actually know the truth completely. Not yet, anyway..."

As EastEnders fans know, Kat gave birth to twins at the age of 14 after being raped by her uncle Harry. Daughter Zoe was raised as Kat's sister, but now it transpires that her son was taken by the Dolan family to live in Ireland.

The trouble is that Dermott obviously has a murderous streak, having let his adoptive mum drown 23 years ago before doing away with Lance in the present day. 

Speaking about his decision to reveal the identity of Kat's son, executive producer Dominic Treadwell-Collns said: "We wanted the audience to be saying, 'run away, Kat and Alfie! Go back to Spain! As we know, Dermott is Harry's son - so there are demons and darkness there.

"How much Harry is there in him? How much bad blood is there? That's an interesting story to tell."