Yesterday, the 89-year-old leader of the party said publicly, "I would struggle for the upliftment of the oppressed communities all my lifetime and to the question 'who after that', don't forget M K Stalin is the answer."
His remark was seen as a declaration that he has picked his younger son, M K Stalin, as his political successor.
That doesn't appear to have gone down well with Mr Karunanidhi's older son, M K Alagiri, who is a union minister. "Our Thalaivar (leader) has already said DMK is not a mutt (sect) to appoint a successor."
The DMK is the biggest ally of Dr Manmohan Singh's government.
While Mr Alagiri was deputed to the Centre as a minister, Mr Stalin has been playing a starring role as the third most senior officer of the DMK. He was deputy chief minister when his father was in power in Tamil Nadu. Recently, he was sent to a session of the United Nations in New York to hand over a party resolution supporting Sri Lankan Tamils, a politically powerful and emotive issue in Tamil Nadu. His father praised his representation by saying, "Stalin has fulfilled his expectations."
Mr Alagiri has a strong following in the southern districts of Tamil Nadu. His supporters, who refer to him as "our braveheart" have praised him repeatedly for proving his strength by helping the party win seats in the South in local and state elections.
Three years ago when Mr Karunanidhi contemplated retirement from active politics in a reported bid to hand over the party to his younger son, Mr Alagiri's tough stand forced him to change his mind. Mr Alagiri had openly said, "I cannot accept anyone as DMK chief other than my father and if there was elections to select the DMK President after his lifetime, I would contest."
Mr Stalin has yet to react to his father's announcement. But his supporters aren't happy. They say the party chief has made it amply clear that Mr Stalin will not take charge of the DMK during Mr Karunanidhi's lifetime.
Some DMK sources say Mr Alagiri had planned a show of strength in Madurai on his birthday later this month. Ahead of that, Mr Stalin wanted a promotion and that allegedly led to his father's controversial announcement yesterday.