Prince Philip’s current title as the Duke of Edinburgh will change after Queen Elizabeth passes the throne to Prince Charles. However, there are some conditions before the change may be put in place.

There are rumors suggesting that Her Majesty will abdicate in 2021 when she turns 95. The move will reportedly favor the heir to the throne, who has been preparing himself for the takeover for the most part of his life.

However, the move doesn’t mean that the monarch would also give up her title as Queen. She will still get to keep it, but she will also be passing on the majority of her duties to her eldest son.

When this happens, Prince Philip’s title will change. He will be referred to as the Guardian of the Queen because of the Regency Act of 1937. The act will only be passed if Prince Philip, along with several other key individuals, will agree that there is sufficient evidence to support Her Majesty’s request.

Royal expert Robert Jobson said that preparations for the transition of the Crown have already begun. One former member of the royal household told Jobson that the Queen’s staff has been ordered to be up to speed on the 1937 Regency Act.

The Regency Act of 1937 will take into effect if there is concrete evidence that will prove that the Queen is no longer capable of performing her royal duties. Once she recovers, she may return to her post. But considering Her Majesty’s age, this may be impossible.

Meanwhile, Prince Philip is not the only member of the royal family whose title will change in the near future. Kate Middleton is rumored to take on Princess Diana’s former title when the Queen steps down.

After the Queen steps down or dies, Prince William and Kate will move up the line of succession. And as such, they will also be undertaking new titles. The Duke and Duchess of Cambridge will now be referred to as the Prince and Princess of Wales.

However, Prince William and Kate will not just inherit their new title. Prince Charles needs to bestow it on them.

Royal Family Prince Charles, Camilla Parker Bowles, Prince Philip, Queen Elizabeth, Prince William and Prince Harry at Madame Tussauds London, Nov. 1, 2016. Luke Rauscher/Flickr