Unnamed sister of Boris

"Symeon Magister records that "Bogaris Bulgarorum dux…sorore sua" was captured by the Byzantines, lived at the imperial court, was converted to Christianity, but was exchanged for the monk Theodoros Koupharas, and tried to convert her brother to Christianity after returning to Bulgaria."

• Source - http://fmg.ac/Projects/MedLands/BULGARIA.htm#GeorgiTerterdied1304