Later Pope Alexander VI (1421-1503)
Blazon: Per pale or a bull passant gules on a base vert within a bordure of the field charged with eight flames of the last and barry of six or and gules*
Rodrigo used these arms at least since his election to the papacy; he may have taken that opportunity to add to his family’s traditional arms. I cannot find any record of the origin of the sinister arms, though several other later Borgias used them as well. They may be a reference to the arms of Aragon, where he was born.
*Also seen as sable