Prince Harry and Prince William joined the other members of the British Royal Family to be with Queen Elizabeth II in Balmoral on Thursday. But, on their trip to Scotland, Meghan Markle and Kate Middleton did not join their spouses as they stayed in London and Windsor, respectively.

Speaking to Entertainment Tonight, Katie Nicholl claimed that, as they understand, the Duchess of Sussex "was not... invited to join the family." She also stated that the former actress "has said she will go to Balmoral another time."

The royal expert noted, as well, that the British Royal Family "wanted [the Duke of Sussex] to be there, even though he was unable to get to Balmoral in time to see [Queen Elizabeth II]." She added, nevertheless, that him traveling on his own and without his wife "is quite significant."

Meghan Markle and Prince Harry have yet to make official statements regarding the matter. So, it is unclear why she was not with her husband on the said trip.

Earlier reports announced, though, that the former actress would join the royal-born Prince on the journey to be with Queen Elizabeth II in Scotland. But, the plans later changed, with Omid Scobie confirming the update on Twitter.

Harper's Bazaar, in its piece covering the matter, quoted the royal expert and author, writing, "A source has [stated] that only Prince Harry has made the trip up to Balmoral. Like the Duchess of Cambridge (who is in Windsor with their three children), [Meghan Markle] is staying back in England (but still not attending tonight's WellChild Awards)."

About Kate Middleton not joining Prince William on the same trip on Thursday, it was reportedly likely because of the pair's three children. People noted that it was the first day of school for the young British Royals in their new school in Windsor.

The magazine recalled that the Cambridge Royals recently relocated from Kensington Palace to Adelaide Cottage on the grounds of Windsor in Berkshire. The move meant a new school for the Duke and Duchess of Cambridge's children, who are now "first-time pupils at Lambrook School."

As a hands-on mother, Kate Middleton reportedly likely stayed behind for the children's first day of classes.

Similar to Meghan Markle and Prince Harry, Kate Middleton and Prince William remain silent as to why she did not join her husband on Thursday's trip.

Meanwhile, the trip to Balmoral came after Buckingham Palace released an official statement about Queen Elizabeth II's health earlier that day.

It said, "Following further evaluation this morning, The Queen's doctors are concerned for Her Majesty's health and have recommended she remain under medical supervision."

It concluded, "The Queen remains comfortable and at Balmoral."