I found that there was a commemorative medal issued for the 100th Anniversary of the Greek Royal family and I am almost 100% sure that this is it. Here is a close-up courtesy of the Orders and Medals Society of America. You can see that the design ties into the close-up of Queen Anne-Marie's brooch as posted by Glenn.
100th Anniversary Memorial Medal of the Greek Royal Family Anamnestikon Sema tes Hekatontaeteridos tes Hellenikes Dynasteias
Instituted: 30 March 1963. Awarded: To guests at the anniversary celebrations in Athens and to those related to the Greek royal house.
Cheers! Bryce
--Previous Message-- : Thanks Glenn : I got distracted between composing the post : and actually posting. : You snuck in before I hit post. : Great minds think alike... : Now all we have to do is figure out what it : is ! : Cheers! : Bryce : : --Previous Message-- : : : --Previous Message-- : I have fond this picture of Queen Anne-Marie : of Greece who seems to wearing the same : brooch. : : Maybe it is commerative or related to the : Order of the Redeemer? : : Any of our Greek experts have any : suggestions? : : : : Cheers! : Bryce : : --Previous Message-- : The picture is also the first photo in the : hardcover Fields ed. 1987, opposite the : title page. I wonder whether the brooch has : a Greek significance, since the picture is : from the return banquet during a Greek state : visit in 1963. Possibly a Greek gift, or : from Prince Philip's family?? : : : : : : :