Prince Charles and Princess Diana
Princess Diana and Prince Charles attend a welcome ceremony in Toronto at the beginning of their Canadian tour on Oct. 1, 1991. Getty Images/Jayne Fincher

Princess Diana’s brother said Prince Charles II lived an “unashamed, self-indulgent” life.

The Princess of Wales’ brother, Charles Spencer, is an author and he has written several royal history books. In his book “To Catch A King: Charles II”s Great Escape ” he covered the abolition of the monarchy and the reign of King Charles II after restoration.

King Charles II had been forced into exile in Normandy and Spanish controlled Southern Netherlands after his father, Charles I, was executed following the English Civil War.

“By early 1685, nearly a quarter of a century into his reign, Charles II's life was one of unashamed self-indulgence,” Spencer wrote. “The fifty-four-year-old monarch had huge appetites for luxury, for food, for drink, and for women. Some of his subjects called him 'Old Rowley' in reference to one of the more fertile stallions in the royal stable.”

He added that Charles II had no legitimate heirs because Catherine Of Braganza was unable to produce him one. However, he had many children from his seven mistresses whom he acknowledged and indulged with varying degree of extravagance.

When Charles II passed away, he was replaced by his younger brother James II as the King of England, Scotland and Ireland.

Meanwhile, Prince Charles might use another name when he takes over the throne. According to royal expert Dickie Arbiter, the Prince of Wales might pick one of his middle names.

“He might choose one of his other names Philip, Arthur or George,” Arbiter said.

According to Richard Fitzwilliams, it’s a custom of the monarch to choose his name and this tradition dates back to the ancient times. However, he also believed that instead of being Charles III, the Prince of Wales might opt to use the name George VII. Using this name would be both a tribute to his grandfather and also to George III whom he admires.

Also, another reason that the Prince of Wales is unlikely to use Charles III is due to the bad reputation of the first two Charles who reigned before him. Prince Charles, himself, had a bad reputation after Princess Diana said that their marriage didn’t work due to his affair with Camilla Parker Bowles.