Prince George once warned classmates that they better "watch out" because his father, Prince William, will one day be king.

"My dad will be king so you better watch out," the eldest son of the Prince and Princess of Wales – and future monarch – once said.

The claim was made in "The New Royals," a book written by Vanity Fair’s royal correspondent Katie Nicholl that’s slated to be released on Oct. 4.

Kinsey Schofield, royal expert and host of the "To Di For" podcast, told Fox News Digital that she isn’t surprised by the claim.

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Prince George Prince William childhood

Comments allegedly made by Prince George, left, sounded similar to what his father Prince William, right, said as a child. (Getty Images)

"While I personally haven't heard any negative stories about Prince George's behavior, it does sound quite similar to Prince William's childhood alter ego, ‘The Basher,’" she said.

According to Schofield, a young William allegedly told a classmate, "My daddy can beat up your daddy… my daddy’s the Prince of Wales."

"He also liked to flex that the queen was his grannie," she shared. "William was considered a cheeky 'terror' at school for his antics. Outlets called him 'noisy' and 'unruly' at the time. Royal experts blamed his upbringing. Then-Prince Charles didn't want William to feel suffocated by discipline and rules while Princess Diana thought his naughty behavior was hilarious."

"The queen inevitably stepped in after young Wills continued to push boundaries," Schofield continued. "She told him that his behavior was unacceptable. You see the queen's influence on Prince William in every aspect of his life today. William is stoic, kind and dedicated to a life of service. We typically hear very sweet descriptions of Prince George's character, but he has been bullied online, so I can't imagine what he has to deal with in real life."

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Prince William childhood

Prince William, who is first in line to the British throne, allegedly used to boast that his grandmother was queen. (Getty Images)

"I wouldn't stop bragging if Prince William was my dad either!" Schofield added.

However, it sounded like William was a handful as a child.

In "The Palace Papers," which was released earlier this year, Tina Brown claimed the queen complained to Prince Philip that her grandson was "out of control."

"She was not amused that he loved to say, ‘When I am king, I’m going to make a new rule that…’" Brown wrote.

Diana, Princess of Wales with her sons, Prince William and Prince Harry

Diana, Princess of Wales with her sons, Prince William, center, and Prince Harry, at the piano in Kensington Palace. Diana's nickname for William was ‘Wombat.’ (Tim Graham Photo Library via Getty Images)

Diana also admitted that her son, whom she nicknamed "Wombat," was turning into "a holy terror – dashing about bumping into tables and lamps, breaking everything in sight."

According to Brown, William allegedly told his nanny Barbara Barnes, "No one tells me what to do! When I am king I will have you punished."
                                                                                                                                       
Nicholl wrote that George is also aware that he will one day be king. The eldest child of William and Kate Middleton, 40, is second in line to the throne. His grandfather, King Charles III, was proclaimed monarch following Queen Elizabeth II’s death on Sept. 8. She was 96.

"They are raising their children, particularly Prince George, with an awareness of who he is and the role he will inherit, but they are keen not to weigh him down with a sense of duty," wrote Nicholl.

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Prince George, Prince William, Princess Charlotte, Prince Louis and Catherine, Duchess of Cambridge on the balcony of Buckingham Palace

Prince George, Prince William, Princess Charlotte, Prince Louis and Catherine, Princess of Wales on the balcony of Buckingham Palace during the celebration of Queen Elizabeth II's Platinum Jubilee earlier this year. (Max Mumby/Indigo/Getty Images)

British historian Robert Lacey said it’s unclear when William spoke to his son about his future royal duties. However, it is believed the conversation may have started around his seventh birthday.

"William’s aim as a father, the prince stressed, was to give his son a normal family upbringing, enabling the monarchy to stay relevant and keep up with modern times," the "Battle of Brothers" author wrote, according to The DailyMail.

William and Middleton also share Princess Charlotte, 7, and Prince Louis, 4.

Mark Tewksbury, a member of the Order of Canada who attended the queen’s state funeral, noted that George and his siblings were "incredibly well-behaved."

"They looked like really incredibly well-behaved kids, but… a little like, 'Wow this is a lot,'" the Olympic swimmer previously told People magazine. "For little Prince George, this will be him one day, and he doesn't really know that yet. And then I thought, 'Ah, he's just lost his great-grandmother.'"

The queen’s death certificate said the monarch died of old age. It was signed by her only daughter, Princess Anne.