My society has a typical line of succession (like the UK monarchy before a female child was given equal status). The eldest son has priority, followed by other sons, and then followed by his daughters.
Unfortunately, the king has died young. He's spent too much time visiting other ladies and has left two children. An illegitimate daughter (who is unaware she's his daughter) and an unborn illegitimate son.
According to most western constitutions would the unborn son be next in line (presumably with an interim ruler) or would the daughter?