1702: End of the personal union between England, Scotland and Ireland and the Dutch Republic, as Willem Friso (no relation to William III) becomes Stadtholder William IV of the Netherlands.
I have two remarks for this section first: William III and Willem Friso were related, they had the same great grandfather, but I can imagine that you consider that not closely related enough. Secondly (and more importantly): When William III died he appointed Willem Friso as his successor, but the provinces of Holland, Zeeland, Utrecht, Gelderland and Overijssel did not accept him as stadholder and so began the second stadholderless era in the Netherlands (eventhough Willem Friso stayed stadholder of Friesland, Groningen and Drenthe)
Thande: I realise that, at least to some extent, but I was oversimplifying as this TL focuses on Britain. I shall add 'claimant' to clarify that his accession did not take place.