The Crowns of Duloc are custom built crowns reserved for the monarchs of Duloc. They were meant to be worn by Lord Farquaad (soon to be "King") and Princess Fiona (soon to be "Queen") when they were married.
The king's crown was briefly worn by Farquaad when he claims that the marriage was "binding;" which in turn made him king of Duloc. His first order however was to lock his queen back in the tower due to her curse. After being eaten by Dragon, she burped the crown out, which fell on the floor.
Crown of the King of Duloc
Crown of the Queen of Duloc