Queen Elizabeth used to wear her Imperial State Crown to bath her kids

Speaking in new documentary 'Coronation Girls', Charles explained: "I remember it all so well then, because I remember my sister and I had bath time in the evening.

"My mama used to come up at bath time wearing the crown to practice. You have to get used to how heavy it is. I've never forgotten, I can still remember it vividly."

He added of the crown: "It is very important to wear it for a certain amount of time [ahead of the coronation], because you get used to it then. But the big one that you're crowned with, the St Edward's Crown, it weighs five pounds.

"It is much heavier and taller, so there's always that feeling of feeling slightly anxious, in case it wobbles. You have to carry it, you have to look straight ahead."

Charles was only four years old at the time of his mother's coronation, but he insisted he still has clear memories of the event.

He said: "My grandmother explained things to me while I was there. I can remember quite a lot, yes, well, particularly what I was dressed in and what the barber did to me before."

The film - directed by Douglas Arrowsmith - follows the story of a group of Canadian women who were hand-picked to attend Queen Elizabeth's coronation with the women returning to the UK to retrace their steps and being invited to Buckingham Palace to meet King Charles.

The group had previously written to Queen Elizabeth to ask for a meeting but she died just months after they sent their note.