The younger brother of Manchester City striker Sergio Aguero has moved to Spain with Cadiz.
Gaston del Castillo, 19, joins Cadiz from Independiente.
The Yellow Submarine will purchase the playmaker for 2.5 million euros at the end of the season, should they take to Castillo in an initial loan spell in Andalusia.
Taking his father's surname, while Aguero uses his mother's surname, Castillo recently appeared for the Argentine youth national side.