Princess Alexandra's necklace also appeared only after Queen Mary's death. And Queen Mary wore one which was remarkably similar.

I floated the idea on the RJWMB at one stage. Jonathan said that he had seen a clearer image of Queen Mary wearing her necklace and seemed to think they were the same, but I have never seen a photo with sufficient definition/clarity which would prove that comprehensively. http://members2.boardhost.com/royal-jewels/thread/1488441399.html