Prester John, the Kalabhras and Mahabali: What is Onam all about?

Prester John myth has been going on in Europe since early 12th century about an Indian Christian King who ruled the three Indias. Very few people have heard really about the Kalabhras who rule as far as central India. No one has any idea who they are. Yet Onam is celebrated with pomp all over Kerala by all religious groups celebrating the rule of a King called Mahabali who was pushed down to hell by Mahavishnu. Is there a connection? This history is revealed by Prof.Ninan