A royal expert says Prince Harry's close relationship with his older brother, Prince William, and sister-in-law, Kate Middleton, changed when he married Meghan Markle.

Ingrid Seward, a royal biographer and Majesty magazine editor, discussed the Sussexes' relationship with the Waleses. She recalled Prince Harry's close relationship with Prince William and Middleton. The three royals were always together and were known as "the royal trio."

"It's something that I could see," Seward told Fox News Digital. "Kate, Harry and [Prince] William were a really close-knit trio. ... They all got on really well. And Harry was constantly around at Kensington Palace having supper with them, borrowing things from their fridge."

According to Seward, Prince Harry's chemistry with the Prince and Princess of Wales changed after Markle joined the picture. Prince Harry reportedly introduced his girlfriends to Middleton, but the two duchesses did not seem to get along.

"Every time he had a new girlfriend, the first person that would meet her would be Kate," the "My Mother and I" author said. "And then Meghan came into the mix, and it was disruptive. It wasn't like the other girlfriends. There [wasn't] that warm feeling. I think it started on the wrong foot."

"Kate wanted to like Meghan, but it didn't work out that way," Seward continued.

Seward previously told The Telegraph, while promoting her recent book "My Mother and I," that "maybe Harry was a little in love with Kate." She clarified that it was a different kind of love, as King Charles' youngest son allegedly desired a sister.

"I don't mean physically, but mentally," she told the outlet. "He always longed for a sister; he told [his mother, Princess] Diana that. Psychologically, I think he just adored her, and he was always there, at Kensington Palace, in their fridge, you know, 'What's for supper?'"

Due to Prince Harry and Middleton's closeness, Seward was convinced that the former "Suits" star had been "incredibly envious and then jealous of Kate." Markle's jealousy could also be due to their disparity in the monarchy as Middleton will be the Queen of England when her husband, Prince William, ascends the throne.

"I heard Meghan actually thought she was going to be a princess and live in Windsor Castle. Instead, there's William and Kate with this beautiful house, while they are stuck in Nottingham Cottage, which Harry used to call 'my hovel,'" Seward said.

According to reports, the Welsh and Sussex families do not get along. Following King Charles and Middleton's cancer diagnosis, many people hoped that Prince Harry and Markle could mend their ties with the royal family.

Tom Quinn, a royal biographer and author of "Kensington Palace: An Intimate Memoir from Queen Mary to Meghan Markle," stated that Prince Harry desired to reconcile with his father and sister-in-law. However, he allegedly was unable to persuade his wife, Markle, to join him because she was still awaiting an apology from the royal family.

However, the Duke and Duchess of Cambridge reportedly had no plans for reconciliation. According to sources close to the Waleses, the "Harry problem" was the last thing on their minds as the King and Princess of Wales battled illness.