Vasily Dimitrov's first name and Nikola Vassileva's surname are both Slavic forms of the name Basil.

From 20000 Names

VASIL (Васил): Bulgarian form of English Basil, meaning "king." VASSILY: Variant spelling of Russian Vasiliy, meaning "king." VASILIOS (Βασίλης): Greek name meaning meaning "king." 74.VASILIS (Βασίλης): Contracted form of Greek Vasilios, meaning "king." 75.VASILIY (Василий): Russian form of Greek Vasilios, meaning "king." [1]

BASIL: English form of French Basile, meaning "king." Also sometimes given as an herb name. 176.BASILE: French form of Latin Basilius, meaning "king." 179.BASILIUS: Latin form of Greek Vasilios, meaning "king." [2]

Βασίλειος seems to translate into our alphabet as both basileios and vasileios [3]. (Vaudree (talk) 12:12, November 9, 2015 (UTC))