Marcus Opellius Antoninus Diadumenianus
Marcus Opellius Antoninus Diadumenianus was the son of Macrinus. Very little is written about this ruler as he never succeeded beyond the role of Caesar. During the reign of his father, he was proclaimed Caesar and the successor of the throne.
However, when Rome turned against his father and the legions of Syria declared Elagabalus the new emperor both father and son were executed and the head of Diadumenian was cut off and presented as a trophy to Elagabalus.