This rather blurry photo from the 1939 French State visit to the UK intrigued me.
When I looked at a video of the visit to the Opera I noticed that what I initially thought was a small brooch on the back of Princess Marina's head looks like a reasonably sized bow brooch. I wonder if this is the ruby bow which was reported to be an alternative centre for the Duke's wedding gift tiara. To my eye this bow looks different from the large Russian bow brooch.
Posters might like to watch the video - it shows lots of glittering jewels.