Grace Kelly’s ‘wild child’ daughter, Princess Stéphanie of Monaco, once ran away with the circus after falling for an elephant trainer

Her relationship with Knie has never been publicly commented on by her family but in private, according to royal biographer Angela Levin, it was not supported.

Levin went on to say Princess Caroline, who assumed many of her mother's roles and duties after her death, was "devastated by her sister's behavior."

"She felt she was letting the whole family down," Levin added.