So in the vision of Paris, it is ruled by an Emperor. This is clearly alternate history, as in 1908, France’s current government is the Third Republic. I was hoping that, perhaps someone more familiar with this part of history than me, could help identify which person is likely to have taken over in this timeline. So let’s go over what we know about this Emperor in Fallen London’s timeline:
[spoiler] For starters, we know that this is a Third Empire, rather than just a Second Empire that lived longer than it did in our world. So that means that the Third Republic was likely established, but then overthrown and replaced by another Empire.
I believe our best bet for identifying a specific person as the Emperor from among all of the other people who could have possibly seized power is by his daughter, the one he seeks to trade Paris for. Her impending death is described as an incurable "wasting disease". This makes me think tuberculosis, as you appeared to "waste away" from that one, and death took a long time. Which means her being the "pale daughter" isn’t another identifying characteristic, but rather just a symptom of her consumption.
So a real world equivalent for the Third Emperor would be someone who could have organized an imperial coup in the Third Republic and lost a daughter to tuberculosis some time around 1908.
[/spoiler]
Most likely it’s Louis-Napoleon Bonaparte, the son of Napoleon III (himself the nephew of Napoleon Bonaparte). Napoleon III ruled over the Second French Empire until his downfall in the Franco-Prussian War in 1871 (the start of the Third French Republic).
At that point he, his wife Eugenie, and his son, Louis-Napoleon moved to England in exile, welcomed by Queen Victoria. There Louis-Napoleon received his military education, and (disempowered) Bonapartists declared him Napoleon IV when his father died.
Itching to prove himself in battle he received special dispensation from Queen Victoria to join British forces in their invasion of the Zulu Kingdom (in modern-day South Africa), where his impatience prompted a scouting party to leave early without a full complement. He kind of took over from the guy who was actually supposed to be in charge, forgot to post a lookout, and was killed in an ambush.
Without Queen Victoria to receive the Bonapartes, it’s possible they found refuge elsewhere. Or without her dispensation, he may not have fought in the British conquest of the Zulu Kingdom.
If he hadn’t died, like his father and great-uncle before him he could have conceivably turned the French Republic into the French Empire, pulling off a Bonaparte hat trick.
Other fun facts!
Queen Victoria’s daughter Princess Beatrice was super into him and there was talk of a possible marriage until his death, which made her and QV a wreck.
His mom Empress Eugénie was besties with Queen Victoria, and the Queen supported the Prince Imperial’s restoration in France.
His childhood nickname was Loulou.
That makes the most sense, and it gives a very simple explanation for history diverging, rather than any more complicated chain of events. He never married in our world, but with Princess Beatrice in the Neath and quite…unsuitable for courtship, that is also explained away.