The titular Maharaja of Travancore Uthradom Thirunal Marthanda Varma, 91, died early on Monday at a private hospital here due to age related illness, doctors said.
Uthradom Thirunal was the younger brother of the last ruling monarch of the Travancore Kingdom Maharajah Chitra Thirunal Rama Varma.
Though having no real administrative power, he held the prestigious post of the custodian of the Padmanabhaswamy Temple, billed as the richest temple in the country.
He is survived by a son and a daughter.
The state government declared a public holiday as a mark of respect to the late Maharajah.
Chief Minister Oommen Chandy who was in Delhi for official work has cut short his trip and will attend his funeral here at his palace in afternoon.
He will be accorded a state funeral.