The biggest television controversy of 2016 kicked off on October 23. Six months previously, hit zombie caper The Walking Dead had signed off on the mother of all cliff-hangers, with newly unveiled super-villain Negan selecting one of the show’s beloved crew of post-apocalyptic survivors for execution.

The torturous twist was that the identity of his victim was to be kept secret until the series returned in the autumn. Who was for the chopping block? Grumpy alpha-male Rick? Mullet-sporting weirdo Eugene? Southern gal Maggie? The tension was excruciating.

As it transpired, Negan would bump off not one but two of The Walking Dead’s regular characters: tough guy Abraham and sensitive dork Glenn. As comparison, imagine Game Of Thrones dispensing with Jon Snow and Ser Jorah Mormont in the same 60 minutes, with no hope of a magic-assisted reprieve. You’d be beside yourself, wouldn’t you?

That wasn’t the sources of the controversy, however. The real shock was the grisly degree to which their deaths were lingered over. Wielding his barbwire-wrapped baseball bat “Lucille”, Negan crushed Abraham’s head to a bloody mulch. It was squelcherific – and almost unwatchable.

Even worse was the fate reserved for Glenn – biffed up so badly by Negan that his eyeball detached from its retina. Viewers were stunned – and many straight-up furious. In the UK, state TV regulator Ofcom received dozens of complaints.

“Tonight’s killing was tasteless and gory and gross,’ railed Forbes magazine. “I’m not sure if this was great drama, or just torture porn.” If The Walking Dead had intended to return with a bang, it had certainly achieved its goal.

“It definitely takes its toll,” says actor Josh McDermitt, who plays Eugene. “We’re trying to tell a good story from a real and authentic place. It’s tough to put ourselves through but it comes across authentically on screen and that’s what matters. It’s an emotional place where you don’t want to spend all your time. That can be really challenging.”

The deaths of Abraham and Glenn were not something anyone involved will forget in a hurry.

“I cried more than I’ve cried at any point in my life during the first half of the season,” says McDermitt.

Yet he rejects the assertion that The Walking Dead has been indulging in blood-letting simply for the shock value.

“We weren’t chanting - ‘more blood, more blood!’ on set. We were having conversations asking, ‘is this too much?’ and we were making decisions that ensured the violence wasn’t gratuitous. I think it was completely justified. With Abraham and Glenn – they are such big characters. They had to go out in a violent manner.”

There’s a lot of hyperbole about television nowadays. Nonetheless it is no exaggeration to describe The Walking Dead as a phenomenon. In the US alone its ratings frequently top 15 million per episode – three times that of Game Of Thrones. What’s especially remarkable is that The Walking Dead, adapted from a hit graphic novel, has become the world’s most popular cable series, despite breaking many of the fundamental rules of binge television.

The show is frequently as slow moving as the undead that totter through corn-fields in the opening credits. The opening half of the previous season, for instance, centred on an infestation of zombies in a canyon near the heroes’ home. How could the charcters remove the walkers without putting human life at risk? Was it better to kill them all – at the cost of desperately-required ammunition – or herd the mob into the wilderness? This is a drama in which logistics matter, which is perhaps the reason why it has struck such a chord with audiences. It never winks or sinks to post-apocalyptic cheese, but examines basic human nature in the face of the destruction of civilisation.

How do the actors deal with the weight of the apocalypse on their shoulders?

“I’m one of those strange people who finds fun in the heavy,” says Seth Gilliam, who plays enigmatic priest Father Gabriel. “I have found it very satisfying to play a character with inner turmoil and I take a great deal of enjoyment in exploring the darker, more troubled side of human nature – then when I leave the set after, it’s almost therapeutic.”

Not everyone relishes delving into the dark side. Austin Amelio, who portrays Negan’s right hand enforcer Dwight, says the episode in which he tries to break hero Daryl with Guantanamo-style torture was one of the toughest jobs he’s undertaken as an actor.

“That was the worst week of my life,” he says. “I was so over it. Every time you’re on set, everybody brings it emotionally. The waves penetrate you. By the end I didn’t want to keep going because it was so hard.”

Amidst the internecine violence and survivor-on-survivor torture, one recurring complaint is that The Walking Dead isn’t terribly interested in the ghouls from which it takes its name. However, there have been steps to address this charge in the latest season, with each episode featuring at least several minutes of slavering zombies.

“It’s tough because they do such a great job with the make-up,” says Ross Marquand, who plays survivor Aaron. “You’re fighting these monsters and you sometimes forget they’re real people and get carried away. When you’re juggling fake knives the last thing you want is to hurt anyone. The challenge is to make it look real without actually inflicting any damage.”

McDermitt is still sporting Eugene’s comedy mullet. Is this a clue that his character makes it to the end of the season alive?

“You want me to spoil everything?” he laughs. “The thing with Eugene pledging his allegiance… He’s fully ‘Negan’ right now. Whether he has intentions that go against that further down the road, I didn’t ask.”

The Walking Dead airs Mondays on Fox.