WARNING: The following contains spoilers for Episode 14 of Moriarty the Patriot, "A Scandal in the British Empire, Part 3," now streaming on Funimation.
Following the introduction of Mycroft Holmes at the end of the anime's first cour, Moriarty the Patriot further expands the famous family in Episode 14 -- the concluding chapter in the "Scandal in the British Empire" arc. When Mycroft, Sherlock's older brother, meets with the Moriarty crime family to come to an arrangement concerning Irene Adler and the dangerous documents in her possession, further details about the secrets said documents contain come to light, including the surprising (and even more secret) connection they have to the Holmes family.
As we learned in Episode 13, the documents divulge the hidden part the British government played in the French Revolution, which the establishment viewed as a social experiment to see how a country led by its citizenry could function. Naturally, should this information get out, it would cause serious damage to Britain's reputation on the world stage -- possibly even inciting a war between it and the other Allied Nations. The current monarchy, headed by Queen Victoria, deems the whole thing to be an ugly blemish on the country's history, and Mycroft, a loyal servant to the Crown, has been tasked with recovering the documents and suppressing the truth at all costs.
In Episode 14, he's taken back to learn that a family as prestigious as the Moriartys, whom Irene has sought refuge with, are behind the 'Lord of Crime''s operations in London, but the two parties nonetheless come to an agreement about how to handle the situation: in exchange for returning the documents and keeping quiet about their contents, the Moriarty family gets to continue culling the Empire's corrupt elites from the shadows, and Irene gets to publically "die," taking on a new identity as "James Bonde" and becoming a member of the gang.
In the process of making this truce, William Moriarty also explains to Mycroft that Maximilien Robespierre -- one of the most important, real-life figures in the French Revolution -- had a huge impact on his own revolutionary thinking. In turn, Mycroft confesses something far more shocking: Robespierre was, in fact, a Holmes -- Sherringford Holmes.
This rewriting of history provides a more personal context for Mycroft's involvement in the case, and for his dogged devotion to serving Queen and country as a sort of penance. The Holmes family's part in toppling France's monarchy obviously isn't something the MI6 Director wants widely known. Even his younger brother is none the wiser. This revelation will probably only heighten William's interest in Sherlock, knowing that he comes from such a storied and rebellious heritage.
Out of universe, though there is no Sherringford Holmes in Arthur Conan Doyle's original canon, Sherrinford (sometimes written as Sherringford) was in contention to be the consulting detective's first name before Conan Doyle settled on Sherlock. Fans of the BBC's Sherlock may also recall Sherrinford was the name of the maximum-security prison in "The Final Problem."
While the exploits of Sherringford Holmes are dead and buried in Moriarty the Patriot's world, a prequel spinoff exploring the character's role as Robespierre during one of the bloodiest and most politically explosive periods in European history would be fascinating to read or watch.