In a 2016 article available here: http://www.irbis-nbuv.gov.ua/cgi-bin/irbis_nbuv/cgiirbis_64.exe?I21DBN=LINK&P21DBN=UJRN&Z21ID=&S21REF=10&S21CNR=20&S21STN=1&S21FMT=ASP_meta&C21COM=S&2_S21P03=FILA=&2_S21STR=kraeznavstvo_2016_1-2_18 Elena Yasynetska proposed that Maria-Dobronega, the wife of Kasimir I the Restorer, duke of Poland, was a daughter of St Boris (a son of St Vladimir the Great, prince of Kiev). Incidentally it was suggested that Agatha may have been a sister of Maria-Dobronega. The name Agatha is traced back to the family of the Byzantine emperor Romanos Lekapenos, along with St Boris' baptismal name Roman, through the latter's mother who is identified as a daughter of Boris II of Bulgaria (a great-grandson of Romanos). The wife of St Boris, the putative mother of Agatha and Maria-Dobronega, is supposed to have been descended from emperor Otto I and his English wife Eadgyth, through their son Liudolf and his conjectured daughter Richlind, duchess of Swabia. I think this is far-fetched, but then there is probably nowhere left except far to fetch another Agatha hypothesis from. St Boris is known to have married at a young age, not long before he and his brother St Gleb were killed, usually placed in 1015 (but possibly in 1017 according to Yasynetska). The hypothesis relies heavily on onomastics and also on a rather forced interpretation of a passage in a 13th-century Polish chronicle, stating that Maria-Dobronega was daughter of the Russian prince Roman son of Odo/Otto ("Kazimirus ... duxit uxorem, filiam Romani principis Russiae filii Odonis nomine Dobronegam, alias dictam Maria"). Yasynetska thinks that Boris-Roman was described as "son of Odo/Otto" as the husband of a descendant of the emperor. She suggests that the connection to St Boris was "carefully hushed up" due to embarrassment by Roman Catholics about descent from an Eastern Orthodox saint. However, in my view this is highly unlikely as the official line was that saints from before the Great Schism (and indeed Russian saints from afterwards) were acceptable in the West. Peter Stewart