In 1865, when
Grand Duke Alexander of Russia died, his fiance
Princess Dagmar of Denmark was greatly distraught, and her family worried about her health; in OTL, she married his brother, the new heir, who went on to become
Alexander III, and their first born son became Nicholas II.
My general idea: Suppose Dagmar dies early 1866, Nicholas II is never born. The other Alexander, meanwhile, somehow dies childless before 1881, when his father is still assassinated. That would mean
this guy -- who I know absolutely nothing about -- becomes Tsar. Except that he has a son,
Cyril, who OTL became pretender to the throne, and a
brother who toured the US and Japan.
How plausible is this? What does this mean for Russia?