A royal expert claimed that being "spare-to-the-heir" means that Prince Harry, and his wife Meghan Markle, may never be popular in the U.K.

Speculations are rife that the Duke and Duchess of Sussex may become working royals again when Prince Charles becomes king. The Prince of Wales reportedly has a soft heart for his youngest son and would want him back in The Firm.

But royal author Ian Lloyd claimed that they would "never shine" as full-time working royals. He said that this is because of the Firm's structure. The 37-year-old is far down the succession line and will always be treated as the "spare" to the throne.

He told The Express, "The problem with being the second is that you grow up with your sibling and you are equal - Diana treated Harry and William as equals, King George VI and Queen Elizabeth treated Elizabeth and Margaret like equals when they were children."

Lloyd, author of "The Queen: 70 Chapters in the Life of Elizabeth II" continued, "But then what happens is that when the older one becomes sovereign or the heir it feels the second sibling more or less disappears."

He explained, "Princess Margaret was second-in-line from 1936 to 1948 and, considering World War 2, Elizabeth could have been killed and Margaret become Queen as a result. But had she lived up to now she would be something like 26th-in-line to the throne, so in other words, she just disappeared off the radars with the passing of the years."

The royal biographer thinks that Prince Harry finds this hierarchy "difficult." He also claimed that the duke and Meghan Markle held "no obvious role" when they were still working royals. He suggested that perhaps the Duchess of Sussex thought she could "make a role and sort of take on the Royal Family but the Palace and the organisation won't do that."

Lloyd claimed that the Firm "only ever support the heir and spare." As such, he said that Prince Harry and Meghan Markle "would never shine" in the U.K. even though they quickly gained a huge following after they started doing public engagements in 2018.

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Prince Harry and Meghan Markle greet the Welsh crowds Getty