Complex sentence: How that widely known image can be traced to the Visconti house is unknown; however, it has been claimed that it was taken from the coat of arms of a Saracen killed by Ottone Visconti during the Crusades.
Split into simpler sentences: How that widely known image can be traced to the Visconti house is unknown, however. It has been claimed that it was taken from the coat of arms of a Saracen killed by Ottone Visconti during the Crusades.