Chola (the first in line to the throne - "aanai mael thunjiya devar") must have brought large-scale disorder in the kingdom.

The second theory has more merit since the sons of Parantaka I (specifically Gandaraditya and Arinjaya) must have also fought along with their brother, Rajaditya in that epic battle and must have been variously injured and died rapidly. Thus, Parantaka I was forced to get his grandson Sundara Chola (the son of Arinjaya and probably the oldest surviving prince) to be the heir-apparent.