Unlike many other systems of law, there was no possibility of post hoc legitimisation of a bastard. If the parents married after the birth, the child would remain a bastard.
One exception to the general principle that a bastard could not inherit, occurred when the eldest son (who would otherwise be heir) was born a bastard, but the second son was born after the parents were married. The eldest son is referred to as a bastard eigne, the second son a mulier puisne.
If the bastard eigne entered onto land of his father and became seised of it until his death, the mulier pusine and all other potential heirs of the father would not inherit, rather heirs of the bastard eigne's body would inherit.
The Provisions of Merton 1235 (20 Hen. 3 c. IX), otherwise known as the Special Bastardy Act 1235, provided that except in the case of real actions the fact of bastardy could be proved by trial by jury, rather than necessitating a bishop's certificate.
In Medieval Wales, prior to its conquest by and incorporation in England, a "bastard" was defined solely as a child not acknowledged by his father. All children acknowledged by a father, whether born in or out of wedlock, had equal legal rights including the right to share in the father's inheritance. This legal difference between Wales and England is often referred to in the well-known "Brother Cadfael" series of Medieval detective mysteries, and provides the solution to the mystery in one of them.