Back in 1987, my mother took my little sister Nell and me to see a new movie she’d read something about in a newspaper: The Bride Princess, she thought, or maybe the The Princess Bride. This movie ended up changing my sister in a way that can only be described as profound. Before seeing The Princess Bride, Nell refused to wear dresses and didn’t much like books; afterwards, she relaxed the tomboyish dresscode and she read William Goldman’s extremely funny original novel, The Princess Bride, so many times that she got told off at school for bringing it in too much.

The reasons Nell loved The Princess Bride exemplify, I suspect, why it has become one of the most enduring and beloved films of all time. Directed by Rob Reiner with a screenplay by Goldman himself, it is ostensibly a simple fairytale: long ago in a far-off land, the most beautiful woman in the world, Buttercup (Robin Wright), falls in love with a farmhand named Westley (Cary Elwes). When she believes he has been killed by pirates, she agrees to marry evil Prince Humperdinck (Chris Sarandon), little knowing that he plans to have her murdered by a band of ruffians (Wallace Shawn, Mandy Patinkin, the wrestler Andre the Giant), masterminded by his wicked friend Count Rugen (Christopher Guest – The Princess Bride has one of the greatest casts of all time, and I haven’t even mentioned Billy Crystal, Carol Kane, Peter Falk, Peter Cook or Mel Smith in this very perfunctory synopsis.) But it’s also a spoof of a fairytale, gently teasing the genre without outright mocking it. Plenty of movies made since take a tongue-in-cheek look at the genre and mix in references for adults – Enchanted and, most obviously, Shrek – but The Princess Bride has a sweetness that Shrek lacks. The Princess Bride never winks over the heads of kids towards the adults, and the kids know it.

So when I read Cary Elwes’ new and highly enjoyable book about the making of the movie, called, of course, As You Wish: Inconceivable Tales from the Making of The Princess Bride (“As you wish” is Elwes’ catchphrase in the film, meaning “I love you”), I knew I not only had to interview him, but I’d have to bring a certain person with me to do the interview. In the end, I brought two: my now thirtysomething sister, Nell, and her three-week-old daughter, Edie.

‘We knew we had a great movie’ … Cary Elwes and Robin Wright in The Princess Bride. Photograph: 20thC Fox/Everett/Rex

The three of us arrive at the publisher’s London office on a bitterly cold morning and Elwes, fresh off the plane from Los Angeles, where he lives with his wife and daughter, eagerly swoops on Edie: “Look at this! This is human Prozac!” he coos in his transatlantic accent (Elwes has primarily lived in the US since he was 18), holding her in his arms. Dear readers, if there is a sight more guaranteed to make a new mother melt than that of her lifelong crush playing with her newborn, then please don’t tell my sister because I am honestly not sure if she will ever get over this encounter. However, after about 20 minutes of my niece hogging the interview, I pull rank and Elwes reluctantly settles down to talk about the film that will, as he happily writes in his book, define him for ever more.

Although The Princess Bride is now one of the most universally adored films, it was a flop when it came out. The studio simply had no idea how to market it. Was it for kids? Adults? Comedy fans? Adventure junkies? In the end, they made it appeal to just about nobody by making a trailer so atrocious it was pulled from cinemas, and a poster so boring it could have been used in clinics for sleep disorders. Aside from some kids whose parents spotted the kid-friendly title, few people bothered to go to see it, and the movie disappeared. This must have been a huge disappointment to Elwes in particular, as it was supposed to be his big break and his first American movie.

“It was – to all of us!” says the still stupidly handsome Elwes, ever so handsomely. “We knew we had a great movie, but it just came and went. I know if social media had been around then it would have caught on, but … ” and he holds his hands up sadly.

It wasn’t until the film came out on home video that it began to grow. Elwes remembers going to get a burger in New York almost a decade after the film’s release. After he gave his order, the waitress said, “As you wish,” and winked at him.

“That was the first time someone did that, and at first I was like: that was odd,” he says.

Presumably there hasn’t been a day since that he hasn’t heard that quote?

“Not really, no.”

Doesn’t he get sick of it?

“God, no! How blessed am I, Hadley, to have been in a film that resonates with so many people? I think I can speak on behalf of the entire cast when I say we all feel blessed by the response this film has now got, because it really didn’t have that response when it came out.”

Cary Elwes in Robin Hood: Men in Tights (1993). Photograph: Allstar/Cinetext Collection

Despite his occasional recourse to LA hyperbole, Elwes was born and raised in London. Inspired by his stepfather, an American film producer, he decided at a young age to become an actor and he studied at the London Academy of Music and Dramatic Art and the Lee Strasberg Institute in the US. His pretty looks were irresistible to casting directors and he was cast in classic British films such as 1984’s Another Country alongside Rupert Everett and Colin Firth, and Lady Jane with Helena Bonham Carter. Elwes’ descriptions in the book of the making of The Princess Bride will immediately make you want to rewatch the movie to see the scenes Elwes had to limp through with a broken toe and fight his 7ft 4in co-star Andre the Giant. “Each time you saw him, it was like meeting him for the first time, in the sense that one could never really become accustomed to his extraordinary size,” Elwes writes. “Memory did not do him justice. He had to be standing there in front of you, blocking the sun or enveloping your hand in his, like an adult taking the hand of a baby, before you really got a sense of what it meant to be in the presence of this impressive human being.” (And any book that includes in the index “Andre the Giant, breaking wind: 123-126” should be required reading for all.)

Since The Princess Bride, Elwes has worked with remarkable consistency in films, and he is most successful when he is sending up his classic swashbuckling looks, as in Robin Hood: Men in Tights and Hot Shots. But he seems genuinely sanguine about still being best known for a movie he made over 25 years ago, and the prospect of answering the same questions from fans and reporters for the rest of his life:

“I know that the epitaph on my tombstone will be ‘As you wish,’ and that’s great!” he grins.

The Princess Bride itself seems to get only more popular every year: when the cast and crew reunited for a 25th reunion in 2012 at the New York film festival, they caused a near-stampede in the audience, and Elwes’ book has already been on the New York Times bestseller list.

Elwes needs to scoot off for a book signing in Piccadilly, but, of course, he has time for a final cuddle with my niece. My sister, who is by now so starstruck she can barely speak, hands over her daughter as if under a spell.

“This is the highlight of my day!” he smiles, and then leans down to whisper in Edie’s ear, “As you wish.”

Who says fairytales don’t come true?