Prince Harry has confirmed on multiple occasions that he is on "different paths" from his brother Prince William, but never revealed the reason behind their differences. A new book written by royal historian and biographer Robert Lacey explores the key incidents that led to the fallout between the once-close royal siblings.

In his book "Battle of Brothers," which is being serialised in The Times, Lacey claims that it was the bullying allegations against Meghan Markle that set off the feud between her husband Prince Harry and his elder brother Prince William. The bullying claims had made it to the news in March this year after two aides who worked for the Duchess of Sussex at Kensington Palace alleged that her unacceptable behaviour drove two personal assistants out of the palace and she "undermined the confidence of a third staff member."

A Kensington Palace courtier has been quoted in the book: "Meghan portrayed herself as the victim, but she was the bully. People felt run over by her. They thought she was a complete narcissist and sociopath — basically unhinged."

According to the book, William tried to confront Harry face to face after he came to know about the "dossier of distress" that had been compiled in relation to Meghan's behaviour, but their conversation led to a bitter row which left both the brothers unhappy with each other. Harry and Meghan used to be part of William and Kate Middleton's Kensington household back then, but the row prompted the Duke of Cambridge to separate their offices and staff.

"The Prince was horrified by what he had just been told about Meghan's alleged behaviour, and he wanted to hear what Harry had to say. The showdown between the brothers was fierce and bitter," Lacey writes in the book about the argument that took place in October 2018, around six months after Harry and Meghan's wedding.

Lacey was told by a friend of the Duke of Cambridge: "William threw Harry out."

According to the royal biographer, William always suspected Meghan to be "hostile" to the royal system and feared that she was planning to leave the monarchy and return to the US from the very beginning. He reportedly told a friend that he believed his sister-in-law had an "agenda" noting that his wife Kate had also been "wary" of her "from the start."

Meanwhile, Harry and Meghan have maintained that there is no truth to the bullying allegations against the Duchess, which made headlines just days before their tell-all interview with Oprah Winfrey in March. A spokesperson for the couple called the claims made to the Times a "calculated smear campaign based on misleading and harmful misinformation."

"We are disappointed to see this defamatory portrayal of The Duchess of Sussex given credibility by a media outlet. It's no coincidence that distorted several-year-old accusations aimed at undermining The Duchess are being briefed to the British media shortly before she and The Duke are due to speak openly and honestly about their experience of recent years," the statement read.

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Prince Harry, Meghan Markle, Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge Chris Jackson/Getty