Both of his parents are experienced tennis players, and his mother in particular was a world No. 1 junior who had a career-high professional ranking inside the top 200 and represented the Soviet Union in Fed Cup.[3] His parents had been working as tennis instructors at the Astir Palace resort hotel in Vouliagmeni at the time of his birth.[2] They originally met at a WTA tournament in Athens where his mother was competing and his father was a line judge.[3] Stefanos has three younger siblings: two brothers Petros and Pavlos (Paul), and a sister Elisavet who is the youngest.