King Charles III has described how Elizabeth II wore her crown during his childhood bath time as practice for her coronation.

“My mama used to come up at bath time wearing the crown to practise,” he said in remarks which will be broadcast in a new documentary.

The King also spoke of feeling “slightly anxious” about wearing the heavy St Edward’s Crown at his own coronation.

The remarks feature in a documentary about a group of Canadian women who attended the late queen’s coronation.

“I remember it all so well then, because I remember my sister and I had bath time in the evening,” King Charles told the women, recalling the run-up to the 1953 event.

“You have to get used to how heavy [the crown] is.

“I’ve never forgotten, I can still remember it vividly.”

He added: “It is very important to wear it for a certain amount of time, 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.”

The 17th Century golden St Edward’s Crown is worn by the monarch at the moment of their coronation and weighs 4.9lb (2.23kg).

But both King Charles III and Elizabeth II wore the Imperial Sate Crown – which weights just more than a kilogram – as they left Westminster Abbey.

The new documentary, Coronation Girls, tells the story of 50 women from across Canada who were sponsored by a Canadian businessman to attend Queen Elizabeth II’s coronation.

It followed 12 of the women, whose average age is 89, as they retraced their steps and returned to London in December last year, where they were surprised by King Charles during a visit to Buckingham Palace.

It is due to air on Boxing Day on WNED PBS in Canada.