Camilla has had an important royal role since she married Prince Charles in 2005.
She has often stepped out with Princess Anne and the royals seem to have a close bond.
However, body language expert Judi James claimed this was not always the case.
When Camilla first joined the family, the expert suggested Princess Anne was “slow to thaw”.
Judi said: “Given their past histories, with Anne having dated Camilla’s ex-husband, the relationship between Anne and Camilla might have been difficult.
“History like that would normally create a sense of embarrassment or discomfort from someone in Anne’s position.
“But [in one photo] she looked as though she might be ignoring or cutting Camilla rather than avoiding her, suggesting she is taking a slow-thaw route to her sister-in-law.
“But now, the two women seem very tolerant of one another to the point of often looking like old friends.”
The expert analysed pictures of the royals at the time and said their body language showed a growing friendship.
She continued: “In 2007, Camilla’s popularity with the public was rising and she was proving her worth as a member of the Firm via some tours abroad with Charles.
“In one photo, sitting in the carriage with Anne, Camilla wears a reasonably relaxed-looking smile.
“It’s the pose of the two women laughing together in the line-up that really seems to signal not just a thawing of the frost between them but a growing sense of close friendship between two women who have so much in common.”
The royal line of succession – who outranks who?
The line of succession to the British throne dictates the order in which each member of the Royal Family would ascend to the throne.
It is also seen as a ranking of importance with the head of the line, the Queen, taking the place of ruler.
Older children come before younger children. Traditionally boys came before girls, but this law was changed on March 26, 2015 before the birth of Prince William’s first child.
Incredibly, Catholics are still excluded from the line of succession, as are children born outside of wedlock.
The royals, who usually stick to a strict protocol when appearing in public, often arrive at events in ascending order of importance, with the most important royal arriving last.
Prince Charles, 72, is currently first-in-line to the British throne, followed by Prince William, 39, his oldest son.
Then comes Prince William’s children, George, seven, Charlotte, six, and Louis, three, and they are followed by Prince Harry, 36. Prince Harry is succeeded by his son Archie Harrison, born in May 2019.