Meghan Markle is said to have found her Windsor walkabout with Kate Middleton and Prince William challenging, according to a new royal book, "Our King: Charles III" by Robert Jobson.

The Duke and Duchess of Sussex had returned to the UK for the Queen's funeral and appeared at a public walkabout at Windsor Castle to meet well-wishers paying their respects.

Jobson's book reveals that Meghan struggled with the day for several reasons, including being away from her children, Archie and Lilibet. He writes, "That's the longest they had ever been away from the kids, and then on top of it, knowing what's being said out there - it was very difficult."

This comes after previous claims that Kate Middleton found the walkabout one of the most challenging things she has ever done. Due to the tension between the senior royal couples following the Queen's death last September, the Princess of Wales is said to have struggled with the time spent together.

Although the walkabout may have appeared as a symbol of unity after the death of the monarchy's centerpiece, Jobson claims that sources informed him that it was not the case. He said such togetherness was an "illusion," and he wrote, "Catherine later admitted to a senior royal that, such was the ill feeling between the two couples, the joint walkabout was one of the hardest things she'd ever had to do."

Relations between the Sussexes and the Royal Family remain strained. Earlier this year, Prince Harry released his memoir "Spare," where he made several accusations against the Royal Family and its senior members. One claim included an alleged physical attack by Prince William. In the Netflix documentary released a month earlier, Harry criticized King Charles as a father and took a swipe at other male members of the Royal Family for their marriage choices.

As the Royal coronation for King Charles approaches, Harry and Meghan have confirmed they received an invitation but have not yet announced whether they will attend. Reports suggest the Sussexes are negotiating their appearance, with The Times stating that they wanted roles for their children, including acknowledging Archie's birthday.