Portugal cedes to Spain Fernando Poo, Annobón and the Guinea coast (modern Equatorial Guinea) in 1778, with the Treaty of El Pardo, signed between Queen Mary II of Portugal and King Charles III of Spain, in exchange for territory in the American continent.

Spain then mounts an expedition to Fernando Poo, led by the Conde de Argelejos, which remains for four months.

In October 1778, Spain installs a governor on the island (who is to stay only until 1780 when the Spanish mission leaves the island).