The tiara belongs to Her Majesty The Queen. It was a gift from the Queen’s parents, King Frederik and Queen Ingrid. Originally, the tiara belonged to Princess Dagmar (1890-1961), the youngest daughter of Frederik VIII and Queen Louise. In 1922 she married Master of the Royal Hunt Jørgen Castenskiold.
Mostly she always has worn the tiara, it’s the only one she has ever worn. Thank goodness she has gotten a new tiara that she might wear shortly (New Year’s Court?)