Page "Ankh-Morpork City Watch" Paragraph 26

While it is common knowledge that Carrot is the true heir to the throne of Ankh-Morpork, he doesn't acknowledge it, and has even hidden evidence of his royal heritage.

The Patrician, Havelock Vetinari, considers him useful for this reason as well as others, as it means that a revolution under the claim of being true heir is impossible, and that if anyone complains that only a king has the authority to do something he does, he can simply refer to Carrot.