Alexis left for Manchester United last month.
Bellerin, speaking at the Oxford Union, revealed: "Alexis is an amazing player.
"One of the best in the Premier League for sure but he is a player who always wants to win.
"He demands from everyone, sometimes it can be too much. The great thing is he wants to win, to give 100 per cent.
"This season maybe things weren't going as well for him but I truly believe he was giving 100 per cent.
"There was one game against Crystal Palace. We celebrated a goal and some of the players went I stayed back, I was talking to Calum Chambers because there was some tactical stuff. For me that was more important than celebrating the goal."