Luc Rousseau is the uncle of Marie-Grace Gardner.
- Name: Luc Rousseau
- First Appearance: Meet Marie-Grace
- Océane Rousseau: Wife
- Thaddeus Gardner: Brother-in-law
- Mama Gardner: Late sister
- Marie-Grace Gardner: Niece
- Daniel Gardner: Late nephew
Luc Rousseau is Marie-Grace's maternal uncle; he is Marie-Grace's mother's youngest brother. He works as a steamboat pilot on the Mississippi River.
Early in the series he is courting Océane Michel, and is married to her at the end of Marie-Grace Makes a Difference.
In Cécile's books, he is referred as Monsieur Luc.