Philippe's older brother, King Leopold II, already had an heir, eight-year-old Prince Leopold. This left Philippe and Marie free to pursue their many religious, literary and artistic interests, while starting their own family. This period of their marriage was very brief, for tragedy struck less than two years later. Young Leopold fell into a pond, developed pneumonia and died. Even then it wasn't entirely clear that the throne would come their way. Leopold and his wife Marie Henriette of Austria were young enough to have more sons. When only another daughter arrived, Philippe's role as heir to the throne was certain.
As the wife of the future king, she did her duty by presenting him with five children: two boys and three girls. Then, tragedy struck again and again, as it so often did in the Belgian royal family. Their baby Josephine Marie died at just two months old and years later, their oldest son Prince Baudouin died of influenza at the age of 21.
Marie clung to her faith, and continued her artistic pursuits. She was even known to exhibit her work.
In the end, however, the throne bypassed Marie. Her husband predeceased his brother. Marie lived long enough to see her youngest child become King Albert I, but passed away at age 67 after battling pneumonia. She was remembered by her family for her tender love, playful spirit, and serious religious convictions.
For more about Marie:
Bonne Maman Flandre on The Cross of Laeken
Marie of Hohenzollern on Maria's Royal Collection
Wedding of Philippe Count of Flanders on Unofficial Royalty