According to a new royal book, Kate Middleton found the joint Windsor walkabout with Prince Harry and Meghan Markle after Queen Elizabeth II's death last year to be a challenging experience due to the strained relationships between the couples.

On September 10, 2022, Prince William and Middleton appeared alongside the Duke and Duchess of Sussex as they greeted mourners outside Windsor Castle in England, marking their first joint public appearance since Harry and Meghan stepped back from their senior royal roles and relocated to California in 2020.

Although the four royals appeared amicable that day, unnamed sources close to the royal family told British journalist and royal correspondent Robert Jobson that the "show of unity" was an illusion.

In his new book, "Our King: Charles III: The Man and the Monarch Revealed," Jobson claims that Middleton later confessed to a senior royal that the joint walkabout was one of the most difficult things she had ever had to do.

Prince William proposed the joint outing in an attempt to present a united front following the death of his grandmother, according to the royal author. However, any goodwill generated by the reunion may have been overshadowed by the Sussexes' Netflix documentary, Prince Harry's memoir "Spare," and subsequent TV interviews criticizing the royal family.

Jobson's book raises questions about how Kate and William might feel about Harry and Meghan now, given their strained relationship. He also suggests that by the time of Queen Elizabeth's death, Harry had very few supporters left in the family.

In September 2022, Kensington Palace announced that Prince William had invited Prince Harry and Meghan to join him and Middleton in greeting well-wishers near Windsor Castle ahead of the Queen's funeral. An unnamed royal source told People that the Prince of Wales believed it was an important display of unity during a difficult time for the family.

Despite the uneasy reunion, the couples reportedly understood the necessity of demonstrating solidarity as the UK mourned the Queen. They are expected to reunite again at King Charles' coronation on May 6th. This week, Page Six reported that plans for Prince Harry and Meghan to travel from California to London for the ceremony are "being finalized."

Jobson's book, "Our King," is set to hit shelves on Thursday.