The 40-year-old mum-of-two said the booze-fuelled sex came after the pair downed ten shots of tequila, Baileys and sambuca.

She says Harry made the first move and this led to them having sex in a field behind The Vine Tree pub in the Wiltshire village of Norton.

They had been in the pub that night to celebrate her 19th birthday.

Because they were such close friends he had bought her a jokey gift of a stuffed Miss Piggy toy and a birthday card which had a joke about a flatulent whale on the front.

And in the pub he bought a tray of 10 shots – five each – which Ms Walpole says made the pair quite very drunk by closing time.

When last orders were called she says he asked her if they should go for a cigarette.

Speaking to Daily Mail she says it went from a kiss to being on the floor pretty quickly and it felt naughty.

She said: “It was instant, fiery, wham bam, between two friends.”

“There were no virgin vibes – he seemed to know what he was doing.”

And she said that it would not have happened if they were not both drunk.

The Sun reports that the pair knew each other from when she worked as a stable girl at Highgrove, King Charles’s country retreat.

And they had been to polo matches several times together.

She says she remembers that he was wearing boxers and that there wasn’t any words spoken between them while it was happening.

And, just like he said in his memoir Spare, she said she did grab his bottom and give him a slap and she said he had a lovely peachy bum.

Ms Walpole said that to her he wasn’t Prince Harry, it was her friend Harry and it was something that got a little bit out of control.