On what date (Gregorian calendar) did Tsar Nicholas II abdicate, signifying the end of the monarchy in Russia?

On the 15th March, 1917, Tsar Nicholas II was forced to abdicate as Tsar, when his train to Petrograd was interrupted by soviets. Prior to this, he had been at the front line (First World War), and was not aware of the extent of anger towards him, acting too late.

This is often called the "February Revolution" because Russia used the Julian calendar at that time, which didn't recognise leap years, so it was actually February in Russia.

He, along with his family, were assassinated on the 17th July, 1918, to prevent the monarchy from being reinstated in Russia.