The Dutch Mellerio Ruby Tiara dates back to 1888; it was a 30th birthday gift from King Willem III to his wife Queen Emma.
"Mellerio" refers to the jewellers who made it; a company of French jewellers called Mellerio dits Meller who were fashionable during the Belle Epoque.
The tiara is part of a parure set made of 961 jewels which were fashioned into a tiara, necklace, earrings, bracelet, jewelled fan, brooch and stomacher.
Here is Queen Maxima of the Netherlands wearing the tiara with the matching earrings and necklace:
And here is Queen Julianna wearing the entire parure set, the only thing missing is the jewelled fan: