I know that after the marriage of the newly enthroned Czar Nicholas II, his mother, the new dowager Czarina Maria Feodorovna, had a run-in with her daughter-in-law, the new Czarina consort, Alexandra Feodorovna, over the Russian state jewels. She refused to hand them over, even after her sovereign son made the request. But Alix was a strong woman with the ability to strike back: she declare them that she would not wear them, anyway ("If motherdear wanted to have the jewels, then motherdear should have them"). Before any public scandal could ensue, the dowager empress submitted the gems.
Flash forward to 1959, and Duke Albrecht of Bavaria, the then-head of the royal house of Wittelsbach, ceremoniously handed the Greek crown jewels back to King Paul of the Hellenes, who in turn accepted them -- according to a Wikipedia article.
My question are: what exactly did the Bavarian royals do with those jewels before then? Who wore them, and why didn't they return them sooner?
Evidently some pieces remain with the Wittelsbachs. I read somewhere that there was a necklace owned by Queen Therese, who bequeathed them to her daughter-in-law Amalia, the queen of Greece. Since the latter had no children of her own, she in turn bequeathed them to her husband's nephew Adalbert, the prince who established the "Spanish" branch of the Wittelsbachs. Evidently it remains with them to this day, as Princess Anna is sometimes seen sporting it.