|Lia de Beaumont|
|Name in Japanese||リア·ド·ボーモン|
|Rōmaji Translation||Ria do Bōmon|
|Voice Actor (Japanese)||Risa Mizuno|
|Voice Actor (English)||Taylor Hannah|
|Relatives|| King Louis XIV (father)|
D'Eon de Beaumont (younger brother)
Maximilien Robespierre (paternal half-brother)
Lia de Beaumont (リア·ド·ボーモン Ria do Bōmon ) was D'Eon's older sister, who was killed under mysterious circumstances. Despite flashbacks of her being a caring and considerate young woman, who was well loved by the nobles and the royals, the spirit that possesses D'Eon is full of great anger, sorrow, and the desire to exact revenge.
When she was alive, she and Maximilien Robespierre were lovers and he asked Lia to marry him, which she happily accepted. But when she read the royal Psalms, she discovers that Maximilien is her half brother from her and D'eon's father's affair with another woman and it devastated her and Maximilien and had to call off their engagement as their union might be considered incest.