Lucilla is the beautiful daughter of Emperor Marcus Aurelius and sister of eventual Emperor Commodus. Lucilla did have a past romance with Maximus, when they were both young and had not yet married. The relationship however ended and Maximus married and had a son, while Lucilla married, had a son and later was widowed. There is still some tension between Lucilla and Maximus, more so on her part since she is now unattached.
Lucilla also allows her brother Commodus to take liberties with her in a more amorous way than between most brothers and sisters. She later explains that she allows him to do so because she is trying to protect her son, Lucius, from Commodus' anger, although she seems to care for him in some small way. She tells no one that he killed their father and voluntarily comforts him when he is upset.
Lucilla later conspires with Senator Gracchus to remove Commodus from power after he grows more unbalanced and dictatorial. She personally goes to Maximus and convinces him to lead his army into Rome against Commodus. Commodus learns of the plot and has Lucius in his lap when Lucilla returns home. He threatens harm to Lucius and Lucilla backs out of the plot and when Maximus goes to escape, he see Senator Gracchus hung to death. After, Commodus receives the news that Maximus was successfully captured, Commodus threatens Lucilla and tells her that if she doesn't comply and obey his order she will kill her son Lucius. Commodus also informs Lucilla that she will sleep with him and provide him and heir of royal blood. Commodus then says "Am I not merciful", to which Lucilla doesn't give a reply. This enrages Commodus who grabs her chin and yells "Am I not merciful". In the Coliseum, she orders the people to honor Maximus and not Commodus following their deaths.