Complex sentence: After Coloman repudiated her on a charge of adultery, Eufemia fled to Kiev, where she gave birth to a son, Boris, who was never regarded as Coloman's son by his Hungarian relatives.
Split into simpler sentences: After Coloman repudiated her on charge of adultery, Eufemia fled to Kiev. Here she gave birth to a son, Boris who was never regarded as Coloman's son by his Hungarian relatives.