BJP leader from West Bengal Rajib Banerjee returned to the Trinamool Congress on Sunday at a rally of party national general secretary Abhishek Banerjee in Agartala in Tripura.
Mr Banerjee, a former minister in the Mamata Banerjee government, said he "repents" for joining the BJP ahead of the Assembly elections despite being asked by the West Bengal Chief Minister not to leave TMC.
He was named BJP's national executive committee member weeks ago and unsuccessfully fought the assembly polls from Domjur in Howrah district.
"I realised that I cannot accept the politics of hatred and divisive ideology propagated by BJP. I cannot accept the anti-people policies of the BJP," he said.
"I had often aired my opinions to the BJP leadership and criticised the personal attack and slander on Mamata Banerjee but no one listened," he added.
Mr Banerjee claimed that he left the TMC due to a misunderstanding, and joined the BJP after being swayed by its blitzkrieg ahead of the polls.
"All these promises were lies and I cannot be a party to them anymore," he said.
"I am sorry and repentant now. I will work under the leadership of Mamata Banerjee and Abhishek Banerjee," he said.
Mr Banerjee was not seen in any BJP programme after the election results were announced on May 2, and has often criticised the BJP leadership publicly.
