Prince Philip once joked that he and Queen Elizabeth would look like "Mr and Mrs Beckham" if they sat on throne-like chairs at the monarch's Diamond Jubilee celebrations

Gyles shared: "Prince Philip was a funny man who liked to laugh and make others laugh. Asked why he and the Queen hadn't sat in the throne-like chairs provided for them during the 2012 Jubilee River Pageant, his wry comment was: 'We'd have looked like Mr and Mrs Beckham, wouldn't we?'

"He knew that he was often portrayed as 'a cantankerous old sod' (his phrase, not mine), but pointed out: 'You arrive somewhere and you go down that receiving line ... I get two or three of them to laugh. Always.'"

The 73-year-old biographer thinks there are some similarities between the duke and his grandson Prince William.

He explained in the Daily Mail newspaper: "I very much enjoyed his company. Having observed him many times at close quarters, I also noticed that the more unassuming people were, the friendlier he'd be.

"Once, coming down the back stairs with him after some lunchtime function at a club in central London, we passed the kitchen. The duke stopped, turned back and marched in, unannounced, to meet the chefs and dish-washers.

"There was laughter, back-slapping, joshing: an enviable display of people skills and unselfconscious charm. The only time I've seen it quite as well done was recently - by Prince William.

"Indeed, with the general public, on the whole, and with those he met undertaking his array of public duties, the duke was surprisingly equable: easy-going, unaffected and good-humoured."