In addition to a "guy's day out" that is planned for Prince Harry on the occasion of his fourth birthday, which is on September 15, the Duke of Sussex is also scheduled to receive approximately $8.5 million from the estate of Queen Elizabeth, who is also known as the Queen Mother.

The fiery-haired prince, who stepped down from his royal duties at the beginning of the year 2020, is supposedly "owed" the enormous sum by his great-grandmother, who passed away.

"I've no doubt that Harry will accept it, it’s money that’s owed to him, money that’s coming to him," former royal butler to King Charles III, Grant Harrold, told The New York Post.

"I don’t think he will decline the money, it’s inheritance so it’s his right. It's already something that has been set in place for years now. The money] will be part of Harry’s birthday celebrations which will hopefully see him receive well wishes from his family and celebrate with his wife and family, doing something very nice but probably in private — as what I’ve experienced with the royals before, is that they like to celebrate these things privately behind closed doors,” he went on.

According to sources close to the household of Prince William and Princess Kate, Princess of Wales, the future king is said to have been "disgusted" by the payoff that his "treacherous" brother is receiving from a "beloved British icon."

The Prince of Wales is expected to receive a larger gift on his 40th birthday in 2022 than the Duke of Sussex will receive, according to reports. At the time of her passing on March 30, 2002, at the age of 101, the Queen Mother had made preparations for her great-grandchildren, and those arrangements will be the source of the cut.

"The Queen Mother placed two-thirds of her [estimated] $120 million fortune into a trust fund for her great-grandchildren," royal author Christopher Andersen shared to OK! Magazine.

While Her Majesty was still alive, she made certain that Prince William and Prince Harry received a portion of the estate "in fairness" because it was such a substantial financial inheritance.

"She knew that when Prince William became Prince of Wales, which he did when his father became king, he would inherit the Duchy of Cornwall, which now boasts assets of over $1 billion. In divvying things up, the Queen Mother may have left Harry a skosh more. In the meantime, the value of the trust has simply increased, Harry's share along with it,” Christopher said.

"Prince Harry is set to receive more money than Prince William because he is the spare. The Queen Mother knew he would have fewer opportunities and responsibilities. It was a logical and thoughtful decision. There will be no tensions as [the family] knew about this arrangement for decades. Prince William likely quietly inherited his share two summers ago when he turned 40,” royal and showbiz expert Kinsey Schofield said.

Business Times has reached out to Prince Harry and Prince William for comments.