Constantine, 307-337. 24 mm. Follis.
Stuck as FILIVS AVGVSTI c. early to later 309, according to RIC
FL VAL CONSTANTINVS FIL AVG, laureate head right.
GENIO FIL AVGG, Genius standing front, head left, holding patera and cornucopia
RIC Antioch 111

In 308 there were six claimants to imperial power. Galerius persuaded the retired Diocletian to chair the famous conference at Carnuntum in 308 which was intended to straighten out who was to rule where. Constantine and Maximinus II did not get the title they wanted, so Galerius invented this new title and awarded it to Constantine and Maximinus II (and minted it for them at his mints), but both rejected it. Only Constantine had this FIL AVGG title on the reverse, struck under Maximinus II at Antioch who did not strike it for himself. 

For much more about the awarding of the unusual title FIL AVG(G), see my page:

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