Prince William "gets on brilliantly" with sister-in-law Pippa Middleton, apparently

When you marry into another family, it can often lead to conflicts — not so with the Windsors and Middletons, according to one royal expert at least.

As Pippa Middleton celebrated her milestone 40th birthday on 6 September, various publications looked into the author and socialite's life and her relationships with various members of the Royal Family.

Apparently, Pippa is really close to older sister Kate, and she also loves brother-in-law Prince William, meaning family relations are super smooth on that side of the family.

"She [Pippa] has proved a loyal and discreet sister-in-law. And that goes a VERY long way in William’s book," explained Jennie Bond, speaking to OK!.

"But she also has the same easy manner and sense of humour that attracted him to Catherine in the first place."

Unfortunately, it's hard not to contrast Jennie's words about William and Pippa's relationship with what we know about where the Prince of Wales stands with his brother Prince Harry at the moment. The two brothers have been all but estranged since the Duke and Duchess of Sussex decided to leave their royal roles, and things don't seem to be getting better.

As for Kate and her own sister, the two are apparently great friends — which won't come as a great shock considering Pippa was her older sibling's bridesmaid for her 2011 wedding.

"She and Catherine are extremely close; they chat as often as possible and meet whenever they can," Jennie revealed.

"They talk about everything, and I very much doubt that Catherine expects her sister to stand on ceremony when they are together.

"In public, of course, Pippa pays due respect to the future Queen, but I suspect they probably both find that sort of protocol quite funny."

While marrying into the Royal Family could have driven a wedge between the once-close sisters, Jenny believes there's a particular factor that helps Pippa not be intimidated by Kate's status.

"The fact that Pippa has married an extremely wealthy man, James Matthews, means that the relationship between the two sisters has remained quite a balanced one," Jennie observes.

Here's hoping William and Harry are able to reconcile in the near future!