Sherlock season 4 episode 1: Steven Moffat explains decision behind devastating twist

A dramatic turn of events rocked the season four premiere

Sherlock fans were left reeling last following a shock twist which saw the death of one of the BBC series' main characters.

Mary Watson (Amanda Abbington) - wife of Holmes' sidekick Dr. John Watson - was the unlucky character after she dramatically took a fatal bullet for Benedict Cumberbatch's titular protagonist.

Co-showrunner and writer Steven Moffat has now addressed his decision to drop such a controversial twist in the season four premiere - a moment some fans aren't convinced by.

He told Entertainment Weekly: "The reality of this, of course, is that Sherlock Holmes is about Sherlock and Dr. Watson and it’s always going to come back to that - always always always. They had fun making it a trio but it doesn’t work long term. Mary was always going to go and we were always going to get back to the two blokes. That’s the format."

Moffat continued, stating the death is no stunt - Mary has actually left the show: "Yes, we’re not playing games. She’s dead."

He seems convinced that his and co-writer Mark Gatiss' decision to kill the character off was wholly warranted.

"...if you just turned dark at the end that would feel like a cheat. You have to feel like you were warned and then forgot the warning. Twists only work if you have a fair chance to work it out. A dark turn in a show only works if you were sort of warned but preferred not to listen.

Previewing the remaining two episodes, Moffat said: "Nobody’s safe and consequences are everywhere and there’s some emotionally gruelling stuff coming. There’s proper humour too. We showed episode two to some people and though it’s the darkest one we’ve ever done there were still people laughing."

Sherlock season 4 continues on BBC One this Sunday.