P. 15, No 32 is the brooch situated under the Northumberland tiara and above one of the so called Marie Antoinette tiaras.
The then owner was Mrs John Wyndham, whose husband was the heir (bar one) to Baron Leconfield, whose heir was John Wyndham's father. Eventually, John Wyndham became Earl Egremont. I am not sure where the brooch originally came from; it is likely to have been a family item from one or other side of the family.
The first photo I found of the brooch being worn was when she was still Mrs John Wyndham and attended the Opening of the Festival of the City of London at the Mansion House in 1962.
Detail.
Thankfully, I found a much better image from July 1965 when, as Lady Egremont, she attended a Gala evening at the Opera House.
Detail
There are a number of references to her wearing this brooch, but fewer photos.
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