Tsar Alexander I was dead to begin with, dead since 1 December in fact. Soldiers of the garrison of St Petersburg and the Imperial Guard had sworn allegiance to his brother Grand Duke Konstantin. However the Grand Duke had never wanted to be Tsar and abdicated in accordance with a secret manifesto signed by the dead emperor that transferred the succession. Into the gap stepped his younger brother Nicholas. Reluctantly at first because he didn’t know about the manifesto and then becasue he wouldn’t accept it.