Queen Margrethe of Denmark is often referred to as "Daisy" as her name is similar to the Nordic word for daisy, "marguerite".
The first Queen Margrethe was the English Princess Margaret of Connaught, who married King Gustaf VI Adolf of Sweden. The Swedes started calling her the English name "Daisy" as an affectionate pun on her name, and a beautiful diamond daisy brooch was made for her.
This she gave to her daughter Princess Ingrid when Ingrid married Frederik of Denmark, who would become King of Denmark. They were the current Queen Margrethe's parents - she was named Margrethe for her grandmother, nicknamed Daisy by the Danes and of course she was given the Daisy brooch.
Here she is wearing it on her wedding day:
And here she is wearing it for her abdication broadcast: