Anthony Head surprised his on-screen son when he showed up to the table read for the new thriller series “The Stranger.”

“I got to play Richard Armitage’s father,” says Head, 65. “Which, bless him — when we met at the read-through he said, ‘You’re too young to play my father!’ I said, ‘Well how old are you? Actually, you were supposed to have been had when me and his mother were 18.’ That actually works out. Literally, mathematically, it’s right.”

Based on a Harlan Coben novel of the same name and filmed in Manchester, England, “The Stranger” (on Netflix) is a British thriller following a family thrown into chaos when they encounter a mysterious figure who reveals unsavory secrets, including secret babies and affairs. Richard Armitage (“Hannibal”) stars as Adam Price, who first gets a visit from the stranger (Hannah John-Kamen, “Game of Thrones”). She doesn’t seem to be doing this for blackmail, or any clear purpose, for that matter.

Head co-stars as Adam’s estranged father, Edgar Price — the instigator on many of the secrets and lies.

“First of all, it’s Harlan Coben. You know straight away that you’re going to get something which is not only a page-turner, but he has such a handle on humanity,” Head says. “All of his ideas are like, ‘Bloody hell, I wish I’d thought of that!’ So as soon as it came through I was like, ‘Yes, whatever, thank you, I’ll do it!’”

Head describes Edgar as a narcissist, a role he relished to play since he doesn’t want to be typecast.

Anthony Head
Anthony HeadPA Images via Getty Images

“It’s something that I’ve worked quite hard at over the years, not to be pigeonholed, for someone to say, ‘Oh that’s him, that’s what he does,’” he says. “It was a really enjoyable character. Ultimately he is the driving force in what’s going on in Adam Price’s life. It’s also a story about a father and son being estranged. I like it when a part develops and grows, and you think it’s one thing and you go, ‘Oh, actually this is going down a very interesting route.’ ”

Head, who will also be seen on Jason Sudeikis’ Apple+ series “Ted Lasso,” is also known for shows such as “Merlin” and “Vanity Fair.” He’s most famous to American TV audiences as Rupert Giles, the Watcher and pseudo-father figure to Buffy Summers (Sarah Michelle Gellar) on cult hit “Buffy the Vampire Slayer” (1997-2003).

“[Fans still bring it up] quite a lot, actually,” he says. “It does span the generations. I still don’t understand how it never came away with any Emmys, or any of those awards. People [tell me] how much it meant to them at the time they were growing up, how it resonated, and bless them. They quite often say Giles was the father figure that was missing in their lives for various reasons. I think that’s part of it’s longevity. It hit home. It’s quite remarkable.

“When we did the pilot … [creator Joss Whedon] said, ‘This is going to be a hit, and it’s not going to be because the powers that be are behind it — they don’t know what they’ve got. It’s going to be something that is made a hit by word of mouth. People are just going to get it and tell each other.’

“And that’s exactly what happened.”

A ‘Buffy’ reboot is in development (with no announced date yet) and Head says he’s game to appear in it, if asked. “Yes. I wouldn’t know what as, because Giles has aged a little bit,” he says. “Maybe I’m the head of the Watcher’s council now. But to be honest, of course I would. It was so formative.”