Prince Harry and Prince William's Relationship Has Hit an 'All-Time Low': Royal Expert (Exclusive)

Royal expert Katie Nicholl discusses with ET the crumbling bond between Prince Harry and Prince William.

It doesn't seem like the relationship between Prince Harry and his older brother, Prince William, is improving.

ET sat down with royal expert Katie Nicholl on Thursday, and she opened up about the status of the connection between Harry, 39, and William, 41.

"Relations between the Sussexes and the Wales remains at an all-time low," Nicholl said. "I'm told that William and Harry really are not even on speaking terms."

This seems to be supported by the invite situation related to the wedding of Hugh Grosvenor, 7th Duke of Westminster, a 33-year-old multi-billionaire, who is tying the knot with longtime love Olivia Henson on Friday.

"There's a big society wedding in the U.K. tomorrow, and both brothers were invited," Nicholl shared. "Harry very diplomatically declined the invite, because he knew it would just be too awkward for him to be even in a venue as large as Chester Cathedral with his brother."

The relationship between King Charles, Prince William and Prince Harry remains rocky, according to royal expert Katie Nicholl. - Tim Rooke - Pool/Getty Images

As Nicholl explained, Grosvenor is "close friends of both William and Harry. In fact, he's godfather to [their children], Prince Archie and to Prince George. So I think he was in a very difficult position when it came to invitations, and of course, seating plans and everything else."

Additionally, William is set to serve as an usher at the wedding of his close friend, which would have only added to the discomfort of the situation.

"Prince William is going to be an usher and that part of that role will be to show other guests to their seats, so you can only imagine how awkward it would be if Harry and Megan turned up, and it was William showing them to their seats," Nicholl mused. "But he won't have to come into any awkward encounters. He'll know many of the people there... William's going to feel very much at home, and will, I'm sure, consider it a great honor to be asked to be an usher. It is it is a privilege."

Prince William meets with Hugh Grosvenor, the Duke of Westminster, the Stanford Hall Estate in Nottinghamshire on June 21, 2018 - OLI SCARFF/AFP via Getty Images

Nicholl said it was also likely Harry's intention was to not overshadow Grosvenor's big day with his presence.

"I think the thing with Harry turning up is, it's always going to generate headlines, and therefore risk overshadowing whatever it is that he's attending," Nicholl said. "I suspect, if you're the groom and and you've got this huge society wedding, that's probably not what you want."

Apart from Harry's rift with William, Nicholl said that "his relationship with his sister-in-law [Kate Middleton] also remains strained."

"I don't believe that there has been much contact, if any at all," Nicholl said, addressing the speculation regarding whether or not Harry and wife Meghan Markle reached out personally to Kate after her cancer diagnosis.

Prince William and wife Kate Middleton attend a gala dinner in England in June 2016. - Stephen Pond/Getty Images

In March, Kate publicly revealed her cancer diagnosis and shared that she would be stepping away from royal duties and public life as she sought treatment.

Kate's health battle has been at the forefront of many people's minds in recent months, and on Wednesday, William joined his father, King Charles III, and Queen Camilla at an event commemorating the 80th anniversary of D-Day in Portsmouth, England, where Kate was noticeably absent from the occasion. 

In a video, posted on X (formally Twitter), William gave an update on his wife's health while speaking to a veteran in a wheelchair who asked if his wife "is getting any better." 

The Prince of Wales sweetly replied, "Yes, she'd love to be here today." 

William's Wednesday outing comes ahead of the royal family's planned appearance for the annual Trooping the Colour military event in June. ET learned that the Princess of Wales, who was appointed the Colonel of the Irish Guards in 2022, will not be at the events and will not do the Colonel's Review. 

In fact, a source told ET last month that Kate is not expected to return to public life until she is cleared by her doctors. There is no timeline for when that could be.