Look. I've said it before and I'll say it again. If Harry has a problem with his family then he needs to persuade the French to fund him, raise an army, invade and seize the crown.

What else was Brexit for, if not to restore traditional British approaches and values?

QUESTION FOR THE EXPERTS: If the French back a Harry-led invasion and seizure of the crown, then he reasserts his right to the French throne, reverse invades and restores the French monarchy in a personal union with the British one...

...does that get us back into the EU?

So what I'm hearing is that the 'Reverse Harry' (not a sex move) will only work if, on seizing the French throne AFTER seizing the British one, he declares the restoration of the Angevin Empire.

That would count as a French successor state, and thus retain EU membership.

Hmmm...

@garius
How about going with something more modern? Tomorrow is January 6. Harry storms the Capitol and reverts the USA, or at least 13 Eastern states, to monarchic rule. He now invades and overruns Canada to the tune of The Star Spangled Banner.
After making French the only official language of Canada he gets French support and can invade England.
This approach is entirely risk-free: AFAICT there is controversy over whether it is even illegal to overthrow the USAian govenment on Jan 6.