Over the past few months, rumors have been swirling that a royal feud has formed between Prince William and his younger brother Prince Harry. Now, royal expert Kate Nicholl has revealed the apparent reason why this feud started, and it involves a warning William gave his brother about his now-wife Meghan Markle.

“I’m told from very reliable sources that the relationship has gone through challenging times since Harry started dating Meghan,” Nicholl explained. “I’m told that privately William was concerned about how quickly the relationship had moved.”

“William wanted to make sure that Harry was making the right decision,” she continued. “And I think what was intended as well-meaning, brotherly concern and a bit of advice went down quite badly with Harry, who felt that William wasn’t being as supportive as he might’ve been. So there has certainly been tensions between the brothers.”

It seems that before Harry’s marriage to Meghan, William had warned him that their relationship was moving a little fast, and his younger brother did not take this well. However, Nicholl was clear that this warning came from a place of love when William gave it.

“William is very protective of Harry,” Nicholl said. “He loves Harry. There has always been an unbreakable brotherly bond… I’m not sure the relationship is what it used to be. But relationships evolve over time and I think theirs was always going to change when Harry married.”

Nicholl also said that she believes the relationship between the brothers will improve in the coming years after Harry and Meghan moved to Frogmore Cottage from Kensington Palace, where William and his wife Kate Middleton reside.

“Moving forward, with the benefit of not living on top of each other at Kensington Palace and with the infrastructure of having their own household, I think the relationship will go from strength to strength from now on,” the expert said. “I hope so because they’re not just two of the world’s most popular princes, they’re two of the world’s favorite brothers.”