Lady Sarah McCorquodale has been left injured following a "very bad fall" during horse-riding

He said on the latest episode of 77-year-old broadcaster Gyles Brandreth's Rosebud podcast: "Sarah, who's nearly a decade older than me, who was always in trouble, she's quite punchy ...

"She's still riding, and she had a very bad fall last month and has been in hospital for a long time. And I think was quite a handful as a patient because the lead doctor said to my brother-in-law, 'She's quite a character, isn't she?'

"Which I think is code for, 'Can you take her home?'"

Charles did not give any further details about Lady Sarah's injuries.

He then told Gyles that his other sister, Jane Fellowes, Baroness Fellowes, 68, is the "complete opposite" of Lady Sarah - who dated the now King Charles, 76.

Charles said: "And then I have another sister, Jane, who's absolutely lovely, the complete opposite, very gentle, very sweet, really funny."

Later in the podcast episode, the 9th Earl Spencer - who regularly talks about Lady Sarah, Baroness Fellowes, and his late sibling Princess Diana - says he often thinks about the former Princess of Wales.

Speaking of Princess Diana - who was killed after a car crash in the Pont de l'Alma tunnel, Paris, France, on August 31, 1997, aged 36 - Charles said: "Particularly anniversaries, you know, and I mean birthdays. 1st July is a big thing.

"My father was very big on our birthdays, so they were a big thing.

"So whenever I got a diary as a child, the first thing that went in were my parents' and siblings' birthdays. And so that's a reminder.

"31st of August is a big day as well. I get fundamentally unhappy on the 31st of August, which is the anniversary of her dying."

Diana is buried on a small tree-covered island in the middle of the Round Oval lake, located within the grounds of the Althorp Estate - the home of the Spencer family - in West Northamptonshire, East Midlands, England.

And Charles regularly visits her.

He said: "I do. Or with any of my children who are there. And we cut flowers and take them to her grave there."