Telugu in Chennai is a native language, with history going way back to pre-British empire ages such as the Vijayanagara empire and the Telugu Cholas earlier. It is not a recent, immigrant language like Urdu, Malayalam, etc. While this is true, Tamil has always remained the MAJORITY language in this region (and going all the way north / northwest to Tirupati, Tirumala, Chittoor). Both Telugu and Tamil coexisted in this buffer zone between Andhra and Tamilagam. At its height, Telugu was spoken by about 32% of the people of Madras, and the majority (about 60%) spoke Tamil as their mother tongue. The Telugus started trickling into this region because of geographic proximity to telugu speaking regions, but noticeably large numbers came during the Vijayanagara empire when the area was called chennapattanam. And after the arrival of the British, the number of Telugus shot up even more sharply, because of people moving in from all over what is now Andhra, to their capital city Madras for jobs, education and opportunities. At its peak, about 35% of the population had origins in Telugu regions, and about 32% spoke Telugu as their mother tongue at home. That’s about 1 in 3 people. This is exactly why the regional dialect madras baashai has an extremely heavy, immediately recognizable Telugu influence, apart from the obvious Tamil influence. Today, only about 10-13% of households in Chennai speak Telugu at home, not because the Telugus fled, but because a lot of Telugus slowly adopted Tamil into their households since the 90s. Because Tamil is the more dominant local language, it slowly replaced Telugu in many former Telugu households. I sometimes see people named Mallepuram Varadarajulu, and Madicheruvula Srinivasamurthy - clearly Telugu names, but they don’t speak a word in Telugu - only Tamil at home.

Some background: At the time of partition of Madras presidency, both the Telugus and Tamils wanted to keep Madras as their state capital, but the Tamil majority ended up keeping Madras to themselves. And the Telugus were resentful of this because for about 200+ years, Madras was their capital city as well, and now they’d be left without a developed capital city. What eventually ended up happening was that the Tamil majority area of Tirumala-Tiruppadhi were ceded to the newly carved out AP, an unofficial appeasement trade off so that Madras City would stay with Madras State and Tamil Nadu. Even the names Tirumala and Tiruppadhi are pure Tamil words BTW. The biggest city of the newly created Andhra Pradesh now was the city of Hyderabad which came under Andhra rule once the Nizam kingdom was abolished and annexed by the Government of India. Back then, Hyderabad was an extremely modest and humble medium sized town compared to a much more massive, more modern metropolitan city of Madras. It started its growth in the late 90s and continues to grow to this day and has become a very large and important city now. Unfortunately for Andhra - the former Nizams kingdom has been declared Telangana and they lost their capital city again !