Unless there is some degree of proof, it would be misleading for an auction house to say a item belonged to a particular person.
In the photo below I have superimposed the modern photo of the jewel being auctioned against the jewel worn by Princess Alexandra.
Has British Royal Jewels given it his imprimatur?
He seemed (at least some time ago) to be working for that firm.
I cannot check as, for my sins, I was blocked some time ago.