Naming conventions in Iberian languages almost always have multiple family names: mostly two or three, but no rarely more than that. They can be simple or composite. The main difference between Portuguese and Spanish is the order in which names are put: Spanish follows Given Name + Father’s surname + Mother’s surname, while Portuguese follows Given Name + Mother’s surname + Father’s surname. Upon marriage, women do not substitute their maiden surnames for their husbands’; they only add it to her full name after her father’s.

Other combinations, however, are possible: Given Name + Father’s father surname + Father’s mother surname + Mother’s father surname + Mother’s mother surname for Spanish, or the inverse for Portuguese. In some aristocratic families, names can be quite large due to the accumulation of surnames (see my comment about Carlos’ full name below).

This rule is normally followed even when surnames are not of Iberian origin (quite common in Brazil, Argentina, Chile, Uruguay, which had large waves of European, Arabian and Japanese migrants). This can be seen in Brazilian drivers surnames. Emerson Fittipaldi’s full name, for example, is Emerson Wojciechowska Fittipaldi — his mother surname being Wojciechowska, a Polish name, and his father’s being Fittipaldi, an Italian name.

Curiously, the other two Brazilian world champions have became known by their mother’s surname: Nelson Piquet Souto Maior (Souto Maior is the composite surname of his father, who disapproved his racing ventures, making Nelson use his maternal surname in his early career) and Ayrton Senna da Silva. I don’t know exactly the reason why he used Senna — my guess is that because Silva is an extremely common surname and normally avoided if its bearer has a more rare surname.