Duke's secret for a long life: Atkins and exercise

Even his decision to finally retire has not been made for medical reasons.

An advocate of healthy eating combined with exercise, he once said he more or less followed the Atkins diet, and he drinks only moderately.

He takes the stairs rather than lifts, and can still fit into the uniform he wore on his wedding day.

He is known for his robust constitution, and told a flu expert at a research centre last year that he had not had the illness for 40 years.

When he turned 82, he decided for the first time not to take part in the Trooping the Colour ceremony on horseback. Instead, he travelled in a carriage with the Queen. He was said to have found previous ceremonies so painful that he had to lie on the floor afterwards to recover.

However, as he advanced into his 10th decade, concerns for his well-being increased, and he faced a series of scares.

Abdominal surgery, bladder infections and a blocked coronary artery have seen him admitted to hospital on a number of occasions.

But despite an operation in 2013, he walked unaided on an official visit to a care home when, at 92, he was older than many of the residents.

Those who suggested he was in poor health were given short shrift. ‘’Do I look bloody ill?’’ he shouted at one estate worker at Sandringham.