Kaloyan of Bulgaria
In 1202, Joan's father, Baldwin IX, left his lands to participate in the Fourth Crusade. After the capture of Constantinople, he was proclaimed Emperor by the crusaders on 9 May 1204. Her mother, Marie of Champagne, decided to join him shortly after his departure, leaving their daughters Joan and Margaret in the care of their paternal uncle, Philip I of Namur. Marie decided to make a pilgrimage to the Holy Land before reuniting with her husband, but died after her arrival at Acre in August 1204. One year later, on 14 April 1205, Baldwin vanished during the Battle of Adrianople against Bulgarians and Cumans under Tsar Kaloyan of Bulgaria. His fate is unknown.