Queen Elizabeth II and Prince Philip have four children, with Anne and Charles being the most similar in age.
However, body language expert Judi James explained they have not necessarily appeared to be “close”.
“Growing up he and Anne perfectly defined the chalk-and-cheese sibling relationship, with Charles suffering through his school years while Anne just got on with things,” Judi told Express.co.uk.
“As Charles adopted a more academic approach to the life of a future King, Anne became a successful, no-nonsense sportswoman alongside her regular royal duties.”
Both royals have attended events on behalf of the monarch for many years but the expert suggested they have shown few displays of a close relationship.
This may have changed in recent years, however, as they have banded together for the Queen.
She added: “There were very little if any relationship-defining poses of the pair over the years, although recently there have been clues that suggest they might have been becoming closer. This might have been prompted by need.
“Senior royals do seems to have closed ranks around the Queen recently, creating an elite squad of Charles, Camilla and Anne, Kate and William and Edward and Sophie.”
Judi continued to say Princess Anne’s seemingly close bond with Charles’ wife, Camilla, Duchess of Cornwall, may also have helped improve their relationship.
Also, Prince Charles’ close relationship with Princess Anne’s daughter, Zara Tindall.
The expert stated: “Given their past histories, with Anne having dated Camilla’s ex husband, the relationship between Anne and Camilla might have been difficult, creating a bigger rift between Charles and his sister.
“But in fact the two women seem very tolerant of one another to the point of often looking like old friends, and this might have created an easing in the relationship between the siblings.
During more recent appearances, and before the coronavirus lockdown, the expert stated they appeared to bond when with their mother.
She concluded: “Recently there does seem to be an element of affectionate humour between Charles and his sister and it will often include their mother.
“Charles still looks very earnest here but Anne’s piercing eye-gaze and grin suggests some gentle mocking.
“That in turn suggests he might not be taking himself too seriously these days.”