Blazon: Argent a cross of Santiago gules between in bend two escutcheons or four palets of the second, and in bend sinister a lion rampant of the last and a castle triple-towered of the third windowed azure
There might be a better way to describe the positioning of the charges, but I’m not entirely sure what that would be. I’m hesitant to say they’re laid out in saltire, since most of them are different, and describing the individual position of each charge (eg. in dexter chief, in sinister chief, etc.) seems excessive. I ended up going with the bends because the charges seem to naturally fall into two groups – the lion and castle of Léon and Castile, and the shields of Aragon for Enrique and Alfonso, Infantes of Aragon.