Tiridates III was the son of
Khosrov II of Armenia by an unnamed mother, the latter being assassinated in 252 by a
Parthian agent named Anak under orders from
Ardashir I. Tiridates had one known sibling, a sister called
Khosrovidukht and was the namesake of his paternal grandfather,
Tiridates II of Armenia.
Anak was captured and executed along with most of his family, while his son,
Gregory the Illuminator, were sheltered in Caesaria, in
Cappadocia. Being the only surviving heir to the throne, Tiridates was quickly taken away to
Rome soon after his father’s assassination while still an infant. He was educated in Rome and was skilled in languages and military tactics;
 in addition he firmly understood and appreciated
Roman law. The Armenian historian
Movses Khorenatsi described him as a brave and strong warrior who participated in the battles against enemies. He personally led his army to victories in many battles.