Charles IV (1748-1819) was King of Spain from 1788 to 1808.
Suppose Charles IV is the Spanish king to 1819.
He still marries Maria Luisa of Parma. However, they are childless.
Now suppose Charles IV has only the younger brother, Infante Gabriel of Spain (1752-1788). Gabriel still marries Infanta Maria Ana Vitoria of Portugal.
They have the one son, Infante Pedro Carlos (1786-1812).
Suppose Pedro Carlos lives numerous years beyond 1812.
Thus Infante Pedro Carlos in 1819 succeeds his childless uncle, Charles IV of Spain.
Shall he be King Charles V of Spain? Or shall he be King Peter V of Spain?
What happens in his reign?