"Your wise moves and hard and sincere work have always kept you very near to the hearts of the people. I am extremely happy that you have staged a brilliant comeback," he said in a letter to the TDP supremo.
Karunanidhi said he had been following the "political growth" of Naidu since the days of his "good old friend," the former Chief Minister N T Rama Rao.
"Under your leadership, I am quite confident that Seemandhra will enjoy a very peaceful and useful governance," he said while wishing Naidu and his party TDP.