More so the last Prime Minister of the United Kingdom of Great Britain and Northern Ireland.
What I'm more interested in is:
What would happen after transfer of sovereignty to the Republic of Ireland?
I know NI will be immediately be back in the EU
But what about the system of law already in NI? It might have to be run as a seperate autonomous area for a set period of time before it can be more integrated with the republic.
Also the Good Friday Agreement should continue to apply in an amended form in the case of a United Ireland.