The Manchester Tiara (not really royal but I can’t help it)
Description: Made up of more than 15,000 diamonds, the Manchester Tiara is considered to be one of the beautiful tiaras in the world. The tiara is gold and silved with diamonds, it is 9.1cm in height, 23.5 in width, and 19 cm depth. The tiara is shaped as heart with C scrolls and is inspired by France before the revolution.
History: Designed by Cartier, the tiara was commissioned by Consuelo, Duchess of Manchester in 1903. The tiara now resides in the Victoria and Albert Museum.
(Thanks to the Victoria and Albert Museum and the BBC for the information. Hopefully I did not make any mistakes)