The DMK has said MK Alagiri stands suspended from all party positions and membership.
Tamil Nadu's best-known political family feud has just climaxed with MK Alagiri being suspended from the DMK, the party headed by his father, M Karunanidhi.
Mr Alagiri, 62, is the DMK chief's older son.
He has been involved in an aggressive and lengthy tug-of-war for control of the party with his brother, MK Stalin.
The DMK said that Mr Alagiri stands suspended from all party positions and membership for indiscipline.
Mr Karunanidhi, who is 89, has been making it clear that Mr Stalin will be his political successor.
In a series of unsubtle moves, Mr Alagiri has tried to contest that, even announcing in 2010 that after his father steps down as party President, the DMK should hold elections for its top post and that he would enter the race.
That mission statement forced Mr Karunanidhi to abandon retirement plans.
The immediate provocation for the action taken today against Mr Alagiri was his vociferous criticism of the DMK's stated interest in allying with another regional party, the DMDK, headed by former actor Captain Vijayakanth.
Mr Alagiri is popular among party workers in and around Madurai. Sources said he is worried that Vijayakanth, who is also well-known and liked in the same area, could deplete his power base.
Recently, Mr Alagiri also challenged the DMK's decision to suspend five workers from Madurai, who allegedly put up posters that were critical of his brother.
(DMK family feud worsens, Karunanidhi suspends five loyalists of elder son Alagiri)