Before the Revolution, the Duma wanted Olga Nikolaevna to be Regent for her brother Alexei. My opinion is that putting Olga on the throne would have been the Czardom's best option (as opposed to best *possible* option... Regency was acceptable, but making Olga N. Empress was impossible in those times. All the men in the line of succession would have screamed blue murder.)
So, Nicholas II, who had been showing signs of heart disease before his death, dies of a heart attack in 1913 and eighteen-year-old Olga N. becomes Regent.