The 28-year-old horse jumper gave birth to the couple's son, Raphael, in December, 2013, but Casiraghi recently called time on the relationship.
A source tells People.com, "It's sad. Mostly, this is a couple that drifted apart over their careers. He wasn't around enough – and she wanted a father for her son."
Rumours of an impending split have been swirling for weeks and Casiraghi fuelled the claims by attending an event at the Cannes Film Festival last month (May15) without the Midnight in Paris star.
News of the notoriously private pair's break up emerged in the French press on Thursday (04Jun15), as Casiraghi prepared to compete in the Saint Tropez Athina Onassis Horse Show, where she suffered a professional knock to her ego as she fell from her horse. She was later seen rubbing her back.
Casiraghi, whose mother is Princess Caroline, is eighth in line to Monaco's throne.
Elmaleh, 44, is also dad to a 15-year-old son named Noe, from a previous relationship with French actress Anne Brochet.