I searched on Google, Wikimedia Commons, ‘The Royal Watcher’, the National Portrait Gallery, the Royal Collection and Getty Images, but was unable to find this photograph. Nor could I identify any of the Duchess’s jewellery that could be adapted into such a tiara.
However, that does not mean it is impossible. The double-row base resembles the familiar construction of the raised Teck Crescent Tiara, which consists of two rivières upon which the base of the tiara sits. In this case, one appears to be a diamond rivière; the second looks to me more like a combination of diamonds and pearls, and above that sits the base of the Teck Crescent Tiara. The upper part is unknown. If genuine, a combination of remnants from something else…
But: given the Duchess’s ‘lack’ of jewellery, it is unlikely that she would have worn it just once. I could not find anything similar in the pictures.
Technically speaking, this photograph is unusually sharp in most areas. I could not find any photograph from this period that is as sharp as this one.
The dress resembles one she wears in other photographs with the Teck Crescent Tiara, but the embellishment at the neckline has been replaced by lace and other details. Not impossible, but why, oh why would she pin a piece of fabric in the shape of a ‘flower’ when she usually wore several orders on ribbons? And why would a woman who wears a large brooch or breastpieces on formal occasions replace it with a fabric bow? I suspect there are some misinterpretations by the AI here.
When I searched for this image on Bing, I got the familiar photos. And the person pictured was identified as Queen Victoria.
Until we can find the unknown tiara, or the jewellery it consists of, or another authenticated image, we should regard it as a forgery.

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I saw this picture of Princess Mary Adelaide wearing an unknown (to me) tiara.
It appears to have some elements of the Teck Crescent tiara, but most of it is unfamiliar.
Has anyone got any information about this tiara, or is this just some AI generated image?
Rob