Rachel Carrington-Matthews, an inheritance protection solicitor at Hedges Law, told Express that the 1717 rule means that the process of inheritance differs greatly for royals.
"In theory, the Queen now would have custody of the royal children and Prince Charles, upon his ascension to the throne, would inherit the custody of the royal children," she said.
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Currently, the Queen could “inherit” two of her grandchildren and all eight of her great-grandchildren in the event of their parent's death.
However, Carrington-Matthews pointed out that it may not be put into practice:
“In practice whether this would be the case would be another issue. It is possible that the royals would have other guidance in place in their wills.”
Regardless of this, the monarch still has input on major parenting decisions for her great-grandchildren, including air travel for heirs above the age of 12.