17/07/2017 03:35 BST | Updated 17/07/2017 19:02 BST

Double Portrait To Mark Duchess Of Cornwall's 70th Birthday

A double portrait of the Prince of Wales and Duchess of Cornwall has been released to mark Camilla's 70th birthday.

Charles and Camilla have been captured by celebrity photographer Mario Testino looking relaxed, happy and smiling.

The royal couple were photographed in May in the morning room at Clarence House, with the Duchess wearing a navy blue dress coat with white embroidery by Fiona Clare, while the Prince wears a suit, shirt and tie.

Testino paid tribute to the Duchess, who celebrates her 70th birthday on Monday, describing her as a "beautiful person".

He was Diana, Princess of Wales's favourite photographer, has taken pictures of the Prince and his sons - the Duke of Cambridge and Prince Harry - several times, and photographed Charles and Camilla to mark their first wedding anniversary in 2006.

The photographer said: "I'm honoured to document their royal highnesses the Prince of Wales and the Duchess of Cornwall on this very important date.

"I first photographed the Duchess after her wedding to the Prince on a commission from British Vogue in 2006, and discovered a kind and beautiful person with a wonderful sense of humour.

"Doing this latest assignment to celebrate Her Royal Highness's 70th birthday is a true honour."

Testino was one of hundreds of guests at a Clarence House garden party on Thursday for the Duchess to acknowledge the people she works with, from charity bosses to celebrities.

In an interview with the Daily Mail, Camilla said she believed hard work was necessary to keep the effects of ageing at the door.

Asked about the arrival of her 70th birthday, she told the paper: 'It is the last thing I want to talk about.

"Truthfully, though, I think if you don't keep your grey cells working and you don't keep going, you'll just sit down and watch the day go by. But if you keep your grey cells working, I think it helps keep you young."

Providing an insight into the physical toll a life of royal engagements can take, Camilla said her footwear could often cause discomfort.

"I'm not sure about being officially old. The trouble is that I don't feel it in my head," she said.

"Sometimes I still feel a teenager, but then other bits of your body don't quite agree. When your feet are screaming in agony at the end of the day, I realise that perhaps, you know, I am getting older."