Technically, we have no idea how it would work. We look to how modern Britain handles it, because FDev is British, and it's a great solution.
But there is absolutely no precedence for a female Emperor, so no precedence for what her potential husband would be called.
Technically, without the marriage, Senator Lavigny is still an illegitimate child of Hegist Duval, and has put her claim to Prince Aristide Lavigny's inheritance in murky waters. It's possible that under Imperial law she has no claim to any inheritance, due to the Prince's sons who were sent to prison for treason during Frontier First Encounters.
From
"Who is the Assassin?" report:
Now that we know that Florence Lavigny, Prince Aristide's wife, was sleeping with Emperor Hengist Duval, a reason for the Lavigny heirs to attempt regicide comes to light. What we don't know is whether these princes are still alive, or if Arissa is now the sole surviving recognised heir of both the Lavigny and the Duval families.
If that's the case, we don't even know what name she will take upon being crowned Emperor, let alone what a potential future husband might be called, or what power he might hold.
Even Queen Victoria's Prince Consort Albert was quite active in British politics, though not in any elected capacity. He was also fairly active in his own duchy of Saxe-Coburg-Saalfeld. The Great Exhibition of 1851 would not have happened without the Prince Consort's active efforts.
