The bandeau has never been worn by reigning Queens. It was not worn by Queen Fabiola and was deliberaty given to Princess Paola, spouse of a younger son (Prince Albert). It was Princess Paola's only real diadem so already almost 60 years ago the choice has been made that this jewel went to a junior line.
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True, Fabiola never wore it. But Queen Paola did, so on that alone you are wrong to say no queen has worn it.
There are 3 queen consorts, 1 wife of a king, and one Crown Princess now queen who have all worn the tiara.
1. Queen Elizabeth, wife of Albert I. The tiara is said to have been made for her.
2. The tiara passed to her daughter in law, Queen Astrid who only wore it a few times before her death.
-It was also worn by Princess Lilian, the second wife of Leopold III (not a queen consort so she didn't make my first count)
3. Queen Paola, worn both as a princess and later when she became queen
The Royal Order of Sartorial Splendor: Tiara Thursday: Queen Elisabeth's Diamond Bandeau
4. Mathilde wore it on her wedding day. Hasn't worn it as queen.
And of course both Princess Astrid and her daughter in law Lili have both worn it as well.
As for your comment about Elisabeth and money, just one of the reasons one hopes it does go to a foundation. One of the sad things is many of these beautiful tiaras end up in auctions. Many of the families need money and end up selling the jewels. You go from saying Astrid has all of these fancy events to attend and needs the jewels, to saying she is basically a common working person. I am getting whip lash here.
As I have said, I have no issue with Astrid wearing. Have said it until blue in my face in fact. I simply wish we would see a trust like in Sweden where the tiaras are maintained within the family. It would allow Astrid and her daughters to have access to the tiara when they needed for events, but would ensure it remained within the family and didn't end up another tiara auctioned off a generation or two down the line as sadly becomes the fait of many.