Difference between Heir Presumptive and Porphyrogenitism

HEIR PRESUMPTIVE vs PORPHYROGENITISM: NOUN

Someone who will inherit only if no better choice for an heir is born.
See heir apparent.
An heir who stands to inherit the estate, title, or office of an intestate ancestor, but whose claim can be defeated if a relative who is closer to the ancestor is born prior to the ancestor's death.
A person who expects to inherit but whose right can be defeated by the birth of a nearer relative

The principle of succession in royal families, especially among the Eastern Roman emperors, by which a younger son, if born after the accession of his father to the throne, was preferred to an elder son who was not so born.
That principle of succession in royal families, especially in the families of the Byzantine emperors, in accordance with which a younger son, if born in the purple—that is, after the succession of his parents to the throne—was preferred to an older son who was not.

Succession, Peacock throne, Kingship, Dynastic, King, Prince consort, Princeling, Monarch, Figurehead, Prince regent, Coronation, Heir, Successor, Throne, Heir apparent

Monarch, Interrex, Imperiality, Holy roman empire, Queen regnant, Aulic, Dapifer, Accessional, Royalize, Successionist, Regious, Interregent, Earl marshal, Royal, Succession

Succession, Peacock throne, Kingship, Dynastic, King, Prince consort, Princeling, Monarch, Figurehead, Prince regent, Coronation, Heir, Successor, Throne, Heir apparent

Monarch, Interrex, Imperiality, Holy roman empire, Queen regnant, Aulic, Dapifer, Accessional, Royalize, Successionist, Regious, Interregent, Earl marshal, Royal, Succession

He is the son of Eliwood, the main character of Fire Emblem: The Blazing Blade, and heir presumptive of Pherae.
Frenchman, that he is not heir presumptive to another crown, and that he has previously taken the civic oath.
Prince Albert became King George VI and the young Princess Elizabeth became heir presumptive to the throne.
Known as "The Brat" in the Heraldic Circle, the Heir-presumptive lives up to her nickname.
Roger was made lieutenant of Ireland and was declared heir presumptive to the Crown.