Peter III was Charles XII's great-nephew as well as Elizabeth's chosen heir. During the war of 1741-43, the Russians proclaimed him king of Finland to exploit that Swedish dynastic connection. The Swedish parliament then considered him heir presumptive without initially realizing that he had already been designated for the Russian throne. The dynastic overlap could have produced a theoretical Swedish-Russian dual monarchy. Sweden withdrew the offer once the conflict between the two successions became clear.
Notable Point · 2:21:53-2:23:49
Peter III almost links the Swedish and Russian successions
Peter III's descent from Charles XII's family made him a claimant in Finland and Sweden even as Elizabeth had already selected him for Russia, briefly raising the possibility of one ruler holding both crowns.