Crispus' year and place of birth are uncertain. He is considered likely to have been born between 299 and 305, somewhere in the Eastern Roman Empire. His mother Minervina was either a concubine or a first wife to Constantine. Nothing else is known about Minervina. His father served as a hostage in the court of Eastern Roman Emperor Diocletian in Nicomedia. Thus securing the loyalty of Caesar of the Western Roman Empire Constantius Chlorus, father of Constantine and grandfather of Crispus.
In 307, Constantine allied to the Italian Augusti, and this alliance was sealed with the marriage of Constantine to Fausta, daughter of Maximian and sister of Maxentius.
The marriage of Constantine to Fausta has caused modern historians to question the status of his relation to Minervina and Crispus. If Minervina was his legitimate wife, Constantine would have needed to secure a divorce before marrying Fausta. This would have required an official written order signed by Constantine himself, but no such order is mentioned by contemporary sources.
This silence in the sources has led many historians to conclude that the relationship between Constantine and Minervina was informal and to assume her to have been an unofficial lover. However, Minervina may have already been dead by 307. A widowed Constantine would need no divorce order.
Neither the true nature of the relationship between Constantine and Minervina nor the reason Crispus came under the protection of his father will ever probably be known. The offspring of an illegitimate affair could have caused dynastical problems and would likely be dismissed, but Crispus was raised by his father in Gaul. This can be seen as evidence of a loving and public relationship between Constantine and Minervina which gave him a reason to protect her son.
The story of Minervina is quite similar to that of Constantine's mother Helena. Constantine's father later had to divorce her for political reasons, specifically, to marry Flavia Maximiana Theodora, the daughter of Maximian, in order to secure his alliance with his new father-in-law. Constantine in turn may have had to put aside Minervina in order to secure an alliance with the same man. Constantius did not however dismiss Constantine as his son, and perhaps Constantine chose to follow the example of his father