A crown was a headpiece usually worn by a monarch symbolising their status. It also referred to the part of the coronation ceremony where the headpiece was placed on the person, investing them with regal authority.
Two versions of the Great Crystal Choir Crown existed in the Doctor's TARDIS, as a result of the Fourth Doctor "borrowing" them two Christmases in a row as a present for Romana II. He planned to return the crowns before they would be missed. (PROSE: Present Tense)
According to history, Edward V of England was technically King of England for a few weeks. However, his uncle prevented him from being crowned on 24 June 1483, instead taking the crown himself. The Fifth Doctor, Erimem and Peri discovered that Edward V was in fact a fiction created by the Tudor-loving William Shakespeare. (AUDIO: The Kingmaker)