Answer:First decline:

After Sadayavarman, his brother Maravarman SUNDARA Pandyan I, came to power in 1216, and he is the one who laid the foundation for the revival of Pandyas monarch. He came to power when the Kulothunga Chola III was aging and almost ruled for continuous 40 years with many expeditions. He managed to march an army against the Mighty Cholas and defeated them at once he came to power. He performed a virabhisekham in the coronation hall of Cholas (mudikondasolapuram) at Ayirattali, Tanjore in the similar way Kulothunga Chola III did. Both Kulothunga Chola III and Rajaraja Chola III was sent to exile. Later Kulothunga Chola III got AID from his son-in-law Veera Ballala II, the greatest monarch of the Hoysala Empire. Ballala sent an army under his son, the crown prince Vira Narasimha II. Cholas accepted the defeat and suzerainty to Sundara Pandyan.

Continuous decline:

After Kulothunga Chola III, his son Rajaraja Chola III came to power in 1216, and he was one of the most incompetent King ever in the HISTORY of Cholas. He has even FLED his capital once, when Pandyas army approached over refusal to pay tribute. Actually, Cholas decline was just postponed every other time only by HOYSALAS intervention. Even one of his own chieftain Kopperunchinga I, captured Rajaraja Chola III, and was only released later after Hoysalas intervention mainly by Vira Narasimha II.

Last Chola:

Last Chola King to rule the shrunken Kingdom was Rajendra Chola III, who came to throne in 1246, and was considered to be an able ruler. Pandyas Empire under Sadayavarman Sundara Pandyan I, continuously expanded its territories. And, Maravarman Kulasekara Pandyan I, defeated Rajendra Chola IIIsomewhere between Trichy and Tanjore. Also he defeated the Pallavas, as Pallavas and Cholas were together fighting against Pandyas in 1279. And there is no evidence for the killing of Rajendra Chola III. But after this war, there is no mention of Pallavas or Cholas anywhere.

Explanation: