With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Flavius Claudius Julianus was born at Constantinople in 331, the son of Julius Constantius, consul in 335 and half-brother of the emperor Constantine, by his second wife, Basilina, a woman of Greek origin. Both of his parents were Christians. Julian's paternal grandparents were the emperor Constantius Chlorus and his second wife, Flavia Maximiana Theodora. His maternal grandfather was Julius Julianus, Praetorian Prefect of the East under the emperor Licinius from 315 to 324, and consul "suffectus" in 325. Historians do not know the exact identity of Julian's maternal grandmother.
text_B: If an historian were to put together a family tree of Flavius Claudius Julianus using current knowledge, would they have to leave a blank space in the grandparents' line?
YES.