Queen Camilla’s sister, Annabel Elliot, has shared a rare perspective on the Queen’s relationship with King Charles.

Describing their bond during a BBC interview for a new documentary, she called Camilla the King’s “rock,” and went on to say she’s the “yin” to his “yang,” adding that theirs is a “brilliant” marriage. She also noted that while Camilla offers unwavering support, Charles has introduced his wife to new “knowledge and interest.”

Richard Jackson, the Bishop of Hereford—one of the two bishops who assisted Queen Camilla during the coronation—also shared his thoughts about the royal couple in the documentary.

He shared his impression, saying: “I think what struck me particularly is how extraordinarily affectionate they are. They’re clearly a very close family of all the generations and in a sense you felt you were part of a family occasion as well as royal occasion and a national occasion.”

Ms. Elliot, the Queen’s younger sister, also reflected on the couple’s bond, noting that even though they have a deep connection, their personalities are quite different.