6: Number of months he and Diana dated before he proposed.
7: Number of official titles — as well as Prince of Wales and Earl of Chester, he is also Duke of Cornwall, Duke of Rothesay, Earl of Carrick, Baron of Renfrew, Lord of the Isles, and Prince and Great Steward of Scotland.
7: According to Jeremy Paxton's 2006 book On Royalty, the number of eggs Charles requests to be boiled for his breakfast before eating just one of them (though the palace says this is totally false!).
7.5: Weight in pounds at birth.
8: Age when both he and his father Philip began boarding at Cheam School in Hampshire.
9: Number of students he shared his dormitory room with at Cheam.