Britain's Queen Elizabeth, Prince Harry and Meghan, the Duchess of Sussex
FILE PHOTO: Britain's Queen Elizabeth, Prince Harry and Meghan, the Duchess of Sussex pose for a picture with some of Queen's Young Leaders at a Buckingham Palace reception following the final Queen's Young Leaders Awards Ceremony, in London, Britain June 26, 2018. John Stillwell/Pool via Reuters/File Photo

Prince Harry and Meghan Markle have yet to announce if they are expanding their family or not, but if they decided to do so, they should know they wouldn’t have full custody of their children. The Duke and Duchess of Sussex will have limited parental control over their future heirs, according to a centuries-old law.

They might be their future children’s parents, but someone else will have the legal custody of them. Just like Prince William and Kate Middleton don’t have the legal custody of their children — Prince George, Princess Charlotte and Prince Louis — Harry and Meghan will also relinquish their rights to their grandmother, Queen Elizabeth II.

Prince George of Cambridge talks to Queen Elizabeth
Prince George of Cambridge talks to Queen Elizabeth outside the Church of St Mary Magdalene on the Sandringham Estate for the Christening of Princess Charlotte of Cambridge on July 5, 2015 in King's Lynn, England. Reuters/Chris Jackson/Pool

“The sovereign has legal custody of the minor grandchildren,” royal expert Marlene Koenig told news.com.au. “This goes back to King George I [who ruled in the early 1700s], and the law’s never been changed. He did it because he had a very poor relationship with his son, the future King George II, so they had this law passed that meant the King was the guardian of his grandchildren.”

The law extended King George I’s right of supervision to his grandchildren, “and this right of right belongs to His Majesty, King of the Realm, even during their father’s lifetime.”

Although it’s more than 300 years old now, the law is still in place because it has never been repealed. This means that George, Charlotte and Louis’ custody belongs to their great-grandmother and not their parents, the Duke and Duchess of Cambridge. And when their grandfather, Prince Charles, becomes king, their legal custody will then belong to him.

It’s not a dormant right as well. Koenig said the Queen has occasionally been known to practise this right. Charles reportedly once had to ask his mother permission for his sons to fly on a plane together to Scotland.

“When [Princes Harry and William] were little, Prince Charles asked the Queen if both children could fly on a plane together to Scotland, to which the Queen said yes,” Koenig told the publication. “Technically, they needed permission for travel. The Queen has the last word on parenting decisions like that.”

Charles, Prince of Wales (L) Prince William, Princess Diana and Prince Harry
FILE PHOTO OF MAY 7, 1995 - Charles, Prince of Wales (L) Prince William, Princess Diana and Prince Harry attend the Heads of State ceremony in Hyde Park to commemorate the 50th Anniversary of VE Day, May 7, 1995. Reuters/Dylan Martinez

Diana, Princess of Wales, was also not allowed to fly William and Harry to Australia shortly before her death because she did not have Her Majesty’s permission. And when she and Charles divorced in 1996, their agreement did not include custody arrangement of their children. It was the same when Prince Andrew and Sarah, Duchess of York, divorced in the same year; the custody of their daughters — Princess Beatrice and Princess Eugenie — were also not included in their arrangement. It’s all because they all did not have the legal custody of their children.

As it was further explained, Diana’s wish for her brother and mother to become William and Harry’s legal guardian in her will was ignored because she did not have the final say on her sons’ upbringing or the “care and control” of them.

Princess Diana holds Prince Harry as her older son Prince William
Princess Diana holds Prince Harry as her older son Prince William (L) looks out over the balcony of Buckingham Palace in London on June 11, 1988 after attending the Trooping the Colour ceremony, the Queen's birthday parade. Reuters/Stringer

Koenig said, though, that the palace “doesn’t make a big deal” out of the old law in 2018. She also doubted Charles would overshadow William and Kate’s decision over their children as he is apparently “very respectful of his son’s parenting.”

“He understands they want to raise their children privately … the only thing Charles might ask for is more picture,” she quipped.

Harry and Meghan should expect the same thing when they become parents as well. The Queen will have legal custody of their children, and this right will be passed on to Charles eventually.