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Catherine the Greaton HBO is catnip for anyone who loves the high stakes, opulence, and semi-Googleable accuracy of a good royal period drama. The first episode of the four-part miniseries, which aired Monday night, deals with the first few years of Catherine The Great's (also known as Catherine II) reign, and while many historical dramas bend the truth in favor of crafting a good story, the violent main event of the premiere episode is pulled straight from the history books.

The episode opens with Helen Mirren's stately Catherine the Great visiting a prisoner of unknown origins at Shlisselburg and ends with that prisoner's violent death during an ambitious guard's attempt to free him. The show drops a few bits of exposition about the prisoner, including that he's a threat to Catherine's throne, but it doesn't fully expand on why and how this young man wound up jailed.

The truth behind his incarceration is a long story, but the real history behind Ivan VI's death is worth a miniseries of its own.

The first thing anyone needs to understand about the Russian imperial line of succession in this era is that it was, and this is a historical term, a complete shitshow. Most of that can be chalked up to the family drama of Peter The Great, who is mentioned a lot in Catherine the Greatas the iconic ruler who founded St. Petersburg and brought Russia into a new era of scientific and cultural enlightenment.

The first thing anyone needs to understand about the Russian imperial line of succession in this era is that it was, and this is a historical term, a complete shitshow.

So enlightened was Peter the Great that he divorced his first wife, a noblewoman with whom he had a son named Alexei, to marry a peasant maid who later took the Russian Orthodox name Catherine (this is not the Catherine from the show). Catherine and Peter had two daughters, Elizabeth and Anna, who were born out of wedlock and later legitimized, and upon the Tsar’s death a pro-commoner faction of government staged a coup to award the crown Peter’s peasant wife as Tsarina Catherine I.

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Catherine I was the first woman to rule Russia, and that action of coup-ing a man off the throne in favor of an unlikely woman candidate became something of Russian habit for the next hundred years.

For example, after Catherine I died the crown skipped her daughters and went to Peter the Great’s grandson through Alexei. This Tsar, called Peter II, was a child alcoholic who died on his wedding day after ruling for three years. The privy council picked Peter the Great’s niece Anna to rule after him (not Catherine I’s daughter, a different Anna), who became famous for being a maniac who kept a gun by her window to shoot birds whenever she felt like it. Tsarina Anna ruled for a decade before passing the throne to her two-month-old grandnephew Ivan VI, a descendent of Peter the Great’s brother.

SEE ALSO:HBO's 'Catherine the Great' trailer promises blood, drama, and a very horny empress

Crowning a literal infant who wasn’t even descended from Peter the Great was the last straw for a character from the beginning of this story, Catherine I’s daughter Elizabeth. While all the Tsars between her father and Ivan VI were busy underage drinking, window-hunting birds, or being a baby, Elizabeth had been playing a long game by befriending the military regiment that guarded the royal palace. Shortly after Ivan VI and his regent showed up, Elizabeth and her co-conspirators pulled the trigger on anothercoup that deposed the baby and placed Peter the Great and Catherine I’s formerly illegitimate daughter on the imperial throne.

To cement her reign as Peter the Great’s true heir, Tsarina Elizabeth I threw Ivan VI in prison. The baby grew up in captivity and was massively undersocialized, leading the few people who knew of his survival to assume the deposed Tsar had long since gone insane. Ivan lived to be twenty-three years old, surviving Elizabeth and her nephew-heir Peter III — Catherine the Great’s husband.

Ivan VI is the prisoner Catherine II encounters in the first scene of HBO’s Catherine the Great. Their meeting occurs after Catherine had taken at least two pages from Russian history and staged a third coup to overthrow her husband and ascend the throne as a German-born, female ruler who still had reason to fear the last remaining male heir of the previous imperial line.

The circumstances around Ivan VI’s murder in prison are depicted more or less truthfully in Catherine the Great. Vasily Mirovich was a nobody at Shlisselburg prison who discovered the truth behind the mysterious, unnamed “Prisoner #1” and attempted to rescue him from captivity, only to activate secret orders that the prisoner be killed if any attempt at escape were ever made.

Mirovich was executed, Catherine II continued to rule, and the tragedy of the baby Tsar whose short, tortured life was punishment for decisions made when he was two months old became a footnote in Russian history.