Empress of Greece and Constantinople, wife of Alexander, emperor of Constantinople. She was the mother of Alexander and Alis, and grandmother of Cligés.
All Chrétien really tells us about Tantalis, however, are her name and her great sadness when her older son Alexander left for Britain, where he served Arthur for a brief time.
We do not know whether she predeceased her husband the old emperor, or survived him to see Alexander’s return and to lend the help of a medieval dowager empress in raising her grandson.
Source
Cligés | Chrétien de Troyes, late 12th century