Prince William and his younger brother, Prince Harry, were brought up to be the classic heir and the spare in the British royal family. But, when the Duke of Sussex decided to leave the royal fold and set a different path in the United States with Meghan Markle, it became a personal blow to the Duke of Cambridge, according to a royal expert.

Royal journalist Camilla Tominey said that Harry's departure significantly and personally affected Prince William because he thought his brother will remain by his side to help with his royal duties. When William becomes the King of England after their father, Prince Charles, he will ideally need Harry to help him out.

Given the turn of events, however, that will no longer be the case today. In October 2019, Harry himself admitted in a TV interview that he and William are "on different paths."

Tominey said that Harry's absence now puts more pressure on the Duke of Cambridge and his wife, Kate Middleton, the Duchess of Cambridge. The royal expert said that without the Sussexes, the Cambridges will need to step up with their royal work since they have a bigger void to fill.

During the time of old England, the spare was simply considered as the "reserve king" since the turnover in the line of succession was more common. But in the modern royal family, the spare's role became less defined.

For instance, then-Princess Elizabeth, the heir, and her younger sister, Princess Margaret, the spare, took on the same public duties in their younger life. When Elizabeth assumed the throne, she relied on her sister to take on some of her other royal commitments, except her constitutional duties. However, when the Queen gave birth to her own heir, Prince Charles, her sister's role became redundant.

Prince Charles is going sit on the throne one day as well and will ideally need his brother, Prince Andrew to take on his other duties. Princess Anne was the spare for 10 years before Prince Andrew was born but the line of succession, prior to 2013, prioritized male heirs.

With Prince Andrew's scandal and controversies, however, the Duke of York won't likely take on public duties once his older brother is the King of England. So, Prince Charles will likely expect his sister to step up and help carry the load but he also has Prince William as his heir.

Prince William has been doing royal work since he married Kate and he's been training to be the King of England as well. William's situation poses a challenge because his heir, Prince George, is still seven and can't do royal work yet.

Without an adult sibling to help him out, Prince William will have to rely on his wife, his aunt Anne, and maybe even his cousins, Princess Beatrice and Princess Eugenie, to work for the royal family. He could also delegate some royal duties to the Earl and Countess of Wessex, Prince Edward, and Sophie, perhaps until Prince George becomes off-age.