The Crown star Claire Foy has said she thinks the reason the Queen and the Duke of Edinburgh’s marriage has lasted so long is because “they can’t get divorced”.

Foy, who plays the Queen during her early years of being monarch, spoke at the premiere for season two of the Netflix show.

When asked what keeps the royal couple together, Foy said: “The fact they can’t get divorced … um, and the fact that they have a shared sense of humour and deep, deep love and respect for one another.

The Crown Season 2 Premiere – LondonMatt Smith (left to right), Stephen Daldry (second left), Claire Foy (Centre) Peter Morgan (second right) and Vanessa Kirby (right) attending the season two premiere of The Crown at the Odeon, Leicester Square, London (Ian West/PA)

“I think the humour aspect for me is the thing that I’ve always understood as the reason why they are able to enjoy each other’s company and still love each other so much.”

The royal couple celebrated their 70th wedding anniversary on Monday.

The platinum anniversary was marked by a new set of images of the pair, which show them happy and smiling.

Royal platinum wedding anniversaryThe Queen and Prince Philip mark their platinum wedding anniversary (Matt Holyoak)

In season two of the show viewers will see the couple’s relationship hit turbulent times.

Doctor Who star Matt Smith, who plays Philip in the series, said: “It wasn’t an easy time for them but they came through it with grace and dignity and their love intact.”

Show creator and writer Peter Morgan said: “If you’re close to someone for that long you’re going to have ups and downs and I didn’t want the show to duck complicated relationships.”

He said he thought “genuine love” was the ingredient that had kept them together so long.

Season two delves deeper into the character of Philip and the troubles he goes through.

Smith, 35, said: “I love him, I think he’s a rock star, I think he’s got great charisma, I think he’s bright and clever and with it.

“I’m down with Prince Philip. He’s 96 and he’s out there on the carriage still taking his mates for a spin, he’s a rock and roller.”

Season three of the hit show will see the cast rebooted as the characters age.

The new Philip has not been announced, but Broadchurch star Olivia Colman has been named as Foy’s successor.

Morgan said he would not write differently for Colman but added: “After a while when I write Philip I’ve got Matt Smith’s voice in my head, and I need to sort of undo that, and I need to undo Claire’s voice.”

Foy, 33, said she “can’t wait” to watch Colman take over the role, adding: “I can’t wait to see what she does, I just think she’s the most extraordinary actress and human being.”

:: All 10 episodes of season two of The Crown will be available on Netflix on December 8.