The outrage about the sale of the Cartier Diadem is unfair to Princess Lilian. Note that after the death of Queen Elisabeth of the Belgians (1965) it passed to her eldest son, former King Leopold III. Not to her younger son Prince Charles, not to her daughter Queen Marie-José of Italy, not to her grandson King Baudouin, etc. After the death of former King Leopold III (1983) naturally his surviving widow, Princess Lilian, could do with the diadem what she wanted. As so many other Belgian royal ladies did before her, the jewels partly dispersed.
Interestingly, Princess Lilian was related to the Cartier family by marriage. M Jean-Jacques Cartier was her brother-in-law as her sister Lydia was married to him. No doubt that a fine deal was arranged between Princess Lilian and the firm Cartier...
Note also that King Leopold III was not only the father of King Baudouin, King Albert II and Grand Duchess Joséphine-Charlotte. He was also the father of Prince Alexandre, Princess Marie-Christine and Princess Marie-Esméralda. According Belgian law the surviving spouse and the 6 children all had the right on a fair share in the estate of the late King. Auctions often are unavoidable to make a proper division between all the heirs and to overcome succession taxes.