The couple knew each other before either married for the first time.

And in fact, Camilla's great-grandmother was mistress to Charles' great-great-grandfather.

But even their extended families can claim places in each other's affections.

• In early-20th century England, King Edward VII's last love was one Alice Keppel, the married maternal great-grandmother of Camilla (who was later reportedly to say to Charles: "My great-grandmother was your great-great-grandfather's mistress, so how about it?").

• Three-quarters of a century later, Charles enjoyed a friendship with keen horseman and polo player Andrew Parker Bowles.

• Andrew's father, Derek Parker Bowles, had been a close friend of the Queen Mother - Charles' grandmother. She became Andrew's godmother.

• Andrew Parker Bowles once dated Charles' sister, Princess Anne, while Charles and Camilla were an item.

• A generation later, Camilla and Andrew's own son, Tom, had a royal godparent, too - none other than Charles, the man who is about to become his mother's husband.