They were lined up in front of a dug trench and then shot at.
On the night of January 28, 1919, at the behest of the Bolsheviks, three Russian grand dukes were executed: Nikolai Mikhailovich Romanov, Georgy Mikhailovich Romanov, and Dmitry Konstantinovich Romanov. It happened about half a year after the assassination of the last ruling Russian Tsar Nikolai II. and his wife Empress Alexandra with their entire immediate family (son and daughters).
The three great princes mentioned were emperor relatives in the male line and members of the imperial dynasty of the Romanovs. The great princes Nikolai Mikhailovich and Georgy Mikhailovich were brothers, while the Grand Duke Dmitry Konstantinovich was a cousin (they had a common grandfather – the Russian Tsar Nikolai I. Romanov). Three great princes were killed in St. Petersburg, near the fortress of St. Peter and Paul. They were brought there by trucks from the prison and then ordered to remove their coats and shirts, despite the cold (the temperature was well below freezing). They were lined up in front of a dug trench and then shot at. Their fourth cousin, Grand Duke Pavel Alexandrovich Romanov, was also executed at the site a little later, in an unusual way. Namely, because he was ill, he was shot on a stretcher and then thrown into the trench.