This wonderful banner (thank you for such a visual treat, Baxter) jogged my memory, as I have some queries regarding the possibility of other large sapphires belonging to the British royals.
To start with this photo of Queen Mary.
After considering if the large central stone in the tiara could be the emerald currently worn by the Duchess of Gloucester, I suspect it is not, as the diamond frame appears to be different, although this is difficult to judge because of the quality of the definition in the photo of Queen Mary.
Gloucester emerald in the tiara
And
I suspect that Queen Mary is wearing sapphires in the above photo because
(a) she is wearing the pearl collar she purchased from the estate of the Dowager Empress of Russia which has a largish sapphire in the centre. I have never heard of it being worn with an emerald centre stone.
And (b) Roberts in a footnote stated that the Garrards' ledger stated the Gloucester tiara was designed to take Queen Mary's sapphire brooch.
If Queen Mary is wearing sapphires in the first photo, then there are at least 3 sapphire jewels we have not seen for a long time.
1 The large central stone in the tiara 2 The earrings 3 The brooch.
It is perhaps possible that the large central stone, if it is a sapphire, might be the one depicted in Queen Victoria's portrait even though the stone appears to be a slightly different shape.