Cousin of Domitian
Vespasian Junior was the son of Flavius Clemens, and Domitian Junior was the son of Flavia Domitilla and, therefore, were his cousins. Domitian had no heir, so toward the end of his reign, he adopted these two boys. Domitian feared the legitimacy of rival heir Titus Flavius Clemens, who was the nephew of Vespasian and husband of Domitilla. In 95AD, Domitian executed Flavius and exiled his wife to Pandateria on charges of atheism. They may have become Christians. As nothing further is recorded concerning the two boys. Coinage struck in Smyrna (Ionia) (modern-day Turkey) exists but only with Vespasian Junior, not his brother.
Æ16 IONIA, Smyrna (Bare hd dr bust rt/Nike stg rt) (RPC 1028)
Æ17 IONIA, Smyrna (Bare hd rt/Nemesis stg left) fourteen known (RPC 1029)
The Monetary History of the World