Wonderful find Mauriz! It certainly looks like her mother's jewel.
Baroness Beaumont wore other diamond stars brooches as well.
I suspect that these all these star brooches were part of her mother, Ethel, Lady Beaumont's, wedding gifts from her husband. According to the press, he gave Ethel 3 large stars as part of his gifts. I wonder which of Baroness Beaumont's descendants got the other stars?
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The star brooch seems to have been inherited by her eldest daughter Lady Mariegold Jamieson. She wore it at her son Simon's wedding to Lady Laura Margaret Fortescue in 1995