Stalin was delivering a speech on the Cauvery issue and criticising Chief Minister C. Joseph Vijay when members of the audience began chanting "Trisha, Trisha".
He paused, smiled and made an apparent double entendre that was widely interpreted as a reference to actor Trisha, Vijay's frequent co-star and close friend, who has long been linked to him by social media speculation.
The video of the exchange quickly went viral, prompting sharp political reactions.
TVK calls remark 'disgusting'
TVK MLA Rhevanth Charan condemned Stalin's comment, calling it "absolutely disgusting" and accusing him of lowering the standards of political discourse.
"Passing such disgraceful comments against anyone is completely unacceptable. It exposes the mindset, political culture, and declining standards of the clan," Charan said, describing the remark as a new low.
BJP demands arrest
The BJP also launched a strong attack on the DMK leader, with Tamil Nadu BJP chief spokesperson Narayanan Thirupathy demanding his arrest.
"Udhayanidhi Stalin's double-meaning speech about Chief Minister Vijay and Trisha is disgusting, obscene, vulgar and shameful," he said, adding that arresting and imprisoning Stalin "would bring more credit" to Chief Minister Vijay.
BJP leader Vinoj P. Selvam also criticised Stalin, saying it was shocking that a former actor would make such remarks about a fellow artist. He urged the actors' association to condemn the statement.
Fresh row after election defeat
The controversy comes just days after the DMK lost power to Vijay's TVK, which made a stunning electoral debut in Tamil Nadu.
Stalin, who transitioned from acting to politics, has courted controversy before. In 2023, he drew nationwide criticism after comparing Sanatan Dharma to diseases such as dengue and malaria, saying it should be eradicated.
The remarks later came under scrutiny in the Supreme Court.
Following the DMK's recent electoral defeat, Stalin had reiterated his stand on the issue in the Tamil Nadu Assembly.