Camilla, Duchess of Cornwall chose Catherine, Duchess of Cambridge, to take her photo for Country Life magazine

The "enormously relaxed" image features Camilla in the garden of her private home, Ray Mill, in Lacock, Wiltshire, sitting on a bench in a blue and white floral dress and cardigan with her hands on a trug of flowers.

Mark Hedges, the editor of the magazine, revealed Camilla had asked if she could "have a go" at guest editing Country Life - which her husband, Prince Charles has previously done twice - some time ago.

When it was agreed she would take charge of the July issue, senior members of staff visited her at Clarence House for a meeting, with among the topics for discussion being the cover.

Mark told the Daily Telegraph newspaper: "She immediately replied, 'Oh I'd quite like Catherine to do it.'

"I spent the next three or four minutes desperately racking my brains trying to think of a professional photographer called Catherine.

"Then I suddenly grasped what she meant - one of the most amazing things that could happen. I found it one of the easier things to nod my head at."

The editor was delighted with the results of the photoshoot.

He said: "I don't think anyone else would have made her feel so relaxed.

"They didn't bother too much with hair and make-up, they just got some flowers for the garden and got on with it."

Sources revealed Catherine - who frequently takes the family photos of husband Prince William and their three children which are released to mark special occasions - was very involved in the process and put a lot of "thought and effort" into the photoshoot, communicating with the magazine about the kind of shots they wanted.

Camilla had the final say in which would appear on the cover, as well as a second photo featured on the leader page of her walking through forget-me-nots in her garden, but she took advice from both Catherine and Charles on which images to use.

Mark believes the special edition of the magazine, which marks the duchess' upcoming 75th birthday, will show her in a new light

He said: "It shows her interests and passions in a way that has not really been seen before.

"I don't think the Duchess has ever revealed so much about herself."