The journalist recounted that she quietly disposed of the tablet shortly after the incident

Charlotte Griffiths, the Mail on Sunday's editor at large, has published a detailed account of her "short and utterly surreal friendship" with Prince Harry following his defeat in a £50 million privacy case against Associated Newspapers this week.

The 42-year-old journalist claims the Duke placed a tablet in her mouth during a December 2011 dinner party when she was a trainee reporter aged 27.

"From his pocket, he removed a small white pill. Then he held it up to my face, popped it on to my tongue, and said with a smile: 'Now I know I can trust you!'" she wrote in the Daily Mail.

The incident allegedly occurred while both were seated together at a shooting weekend on a 4,000-acre Hampshire estate.

Ms Griffiths described the gathering as including approximately 16 people whom the Prince considered trusted companions.

She portrayed Harry as energetic and charismatic during their encounters, writing: "In person, he was quite the live wire: boisterous, charming and overflowing with a (sometimes excessive) degree of self-confidence."

The journalist also noted his fondness for pranks when surrounded by those in his inner circle, characterising him as "a compulsive practical joker".

Regarding the mysterious tablet, Ms Griffiths recounted that she quietly disposed of it shortly after the incident.

Ms Griffiths wrote: "Take that white pill he’d so brazenly stuck in my mouth (which I discreetly removed and folded into a napkin soon afterwards).

“It was almost certainly paracetamol, rather than something more sinister. But I couldn’t be entirely sure."

Ms Griffiths also revealed that Harry told her he used creatine as a substitute for cocaine during his time serving in the military.

The Duke explained he was subject to random drug testing in the Army, which prevented him from using illegal substances that others consumed at social venues.

"While others might take cocaine at the clubs, bars and parties he went to, he told me he now took something called creatine," she wrote.

The legal supplement, typically consumed by bodybuilders mixed with water, apparently provided similar effects when inhaled as a powder.

Ms Griffiths wrote: "When inhaled in powder form, Harry explained, the stuff provides a burst of energy that keeps one dancing till dawn."

The Duke has previously acknowledged using cocaine, cannabis and magic mushrooms in his memoir Spare.