Prince William and Prince Harry's feud is growing worse by the day.

A new report says the brothers even clashed behind closed doors while Prince Harry attended the funeral of Prince Philip in April. Royal expert Robert Lacey broke the story this weekend, days before the brothers will again reunite for a family ceremony.

Prince William, Prince Harry fought at Prince Philip's funeral

Initially, Prince Philip's funeral was viewed as a possible stepping stone toward the brothers reconciling. After the ceremony, they were even seen chatting together briefly.

But their feud apparently reignited right after that moment, when they entered Windsor Castle and were no longer on camera. In Daily Mail this weekend, Robert Lacey revealed that William and Harry "started quarrelling again" inside the castle "within minutes."

Prince William and Prince Harry at the funeral of Prince Philip in April 2021.

A source told the royal expert that the brothers were "at each other's throats as fiercely as ever." They added, "The rage and anger between those two has grown so incredibly deep. Too many harsh and wounding things have been said."

Lacey, the royal historian and Battle of Brothers author, confirmed that "no reconciliation" happened during Harry's UK trip in April, as had been speculated at the time. But friends and family members are still committed to peacemaking work, the expert added.

Another William-Harry scrap revealed before Diana ceremony

It's a concerning update that comes just days before William and Harry will reunite for another meaningful family event. On July 1, the brothers will together unveil a statue honouring their late mother Princess Diana at Kensington Palace.

Cousin Peter Phillips divided William and Harry at Prince Philip's funeral.

Certainly, no one expects a clash to break out at the ceremony for Princess Diana. But the same could've been said for the funeral of their 99-year-old grandfather in April, even if they made sure to hold off until they were out of view from photographers.

Prince Harry is currently self-isolating at Frogmore Cottage in Windsor ahead of the July 1 ceremony. He and his brother still aren't believed to be on speaking terms, just days before the event honouring what would've been Princess Diana's 60th birthday.

Marlon Brando: The Tragic Life Of His Children

"I think that perhaps I failed as a father"

Marlon Brando: The Tragic Fate Of His Children