A fascinating question was recently posed on a Monarchist discussion board. The scenario is one that we in this Scepter'd Isle shall hopefully never face, nevertheless it raises some interesting issues and I therefore post the question and my reponse:
Q. Can an unborn baby inherit the throne? e.g. the King dies while his wife is pregnant with their son. Will that unborn son inherit or eventually inherit the throne?
As with all such questions, one must first look to the law of succession applicable to the state / house in question. Unfortunately, in the case of our own Monarchy, there is no clear answer.
We must therefore turn to history for guidance. Whilst our Monarchy has never dealt with this scenario, there have been examples on the continent.
Louis X's queen, Clemence d'Anjou, was pregnant at the time of his death in 1316. In what laid the foundation for Salic succesion, Louis' living daughter was passed over and Louis' brother was named regent. 5 months later Clemence gave birth to a boy, who immediately succeeded to the throne as King Jean I. He died a few days later and the regent succeeded as King. Had Clemence given birth to a daughter, the regent, as heir presumptive, would have been named Sovereign retroactively to the date of his brother's death. Something similar occurred a few years later, also in France, with Philip VI's succession to Charles IV in 1328, although Philip's relationship was more distant.
A less ancient case occurred in Spain in 1885, where the law of succession was similar to our own. Upon the death of King Alfonso XII his pregnant queen was appointed regent. Her child was proclaimed King upon birth. We might expect a similar scenario in the case of our own monarchy, although this cannot be guaranteed as the Regency Act permits the establishment of a regency only where a sovereign exists.
Unfortunately we cannot look to any UK legislation for advice as none deals with this specific event. Whilst any answer must therefore be speculative, our own history provides us with one possible solution. Queen Adelaide, William IV's widow, was still of child-bearing age upon his death in 1837. Consequently Victoria was proclaimed queen "saving the rights of any issue of his late Majesty's consort". This proclamation may provide some indication of the manner in which the matter might be handled -- although it is our law-makers who shall have final say.