What is the term when a king first has a son, then a daughter?

Question

Presumably, the combination of a first-born son who inherits the throne and a second-born daughter who can marry royalty from another kingdom was so desirable that there is a phrase the refers specifically to this exact combination of offspring.

I believe the phrase starts as "a king's ..."

Answer 1

a king's dual heirarchy

Answer 2

In America, we might call it,

the "King's Oops",

because they always want

an heir and a spare,

but seriously,

it is what your first answerer replied.

I just couldn't resist the humor.

Answer 3

Princess Royale or Grand Ducchess