While details are still being finalised, sources suggest the separate religious celebration will be held in July at either St. Remy de Province or the Mediterranean island of Pantalleria off Sicily, where the groom’s mother, actress and model Carole Bouquet, maintains a 13-acre vineyard estate.
The couple are the proud parents to 5-month-old Balthazar.
Casiraghi, the eldest granddaughter of Princess Grace, has never been married.
She also has a 5-year-old son Raphael from a previous relationship with comedian Gad Elmaleh.
Rassam, who has been married before, has a 7-year-old daughter.