IIRC Boris told us some time ago Queen Sofia's Diamond Tiara - the so-called Nine-Prong - is not that flexible. I believe that one it's not possible to adjust to fit one's head. He gave the example of Princess Birgitta during CP Victoria's wedding.
--Previous Message-- : In principle all diadems can be modified to : fit the bearer best. The one diadem is : ultra-flexible (Leuchtenberg!), the other : maybe requires some more work because it has : been fixed more permanently. : : That is why I was a little bit disappointed : with the way the diadem was worn by Princess : Marie-Chantal. After thirty years one would : think the whole jewel was controlled, : cleaned and fixed to suit the Princess' head : best. It looks like this has not been done. : The picture by Maud shows that the diadem in : any way is quite flexible. : :