BJP MLA Soumen Roy Saturday joined the ruling Trinamool Congress (TMC) and said he was sorry for having quit the state party two years ago.
He is the fourth BJP MLA to have quit the party and joined TMC since the April-May assembly poll.
With his resignation BJP's strength in the 294-member House has reduced to 71.
Mr Roy, who was elected from Kaliaganj on a BJP ticket in the April-May assembly poll in the presence of party secretary general Partha Chatterjee said he was not comfortable in the saffron camp and wanted to take part in the development initiatives by Chief Minister Mamata Banerjee.
"Though I had quit TMC my mind and soul had remained with TMC. I do not subscribe to its ideology," he said.
"BJP MLA Soumen Roy is returning to our fold as he wants to be part of the development of Bengal specially north Bengal," Mr Chatterjee said.
To a question Mr Roy said he was sorry about leaving TMC with which he had been associated for years.
BJP national vice-president Mukul Roy had returned to TMC with son Subhransu in May days after being elected on the saffron party ticket from Krishnanagar South seat.
He was followed by three more TMC turncoats, who had contested the election on BJP ticket, won and returned to their old party.
Reacting to Mr Roy's switching over, state leader of opposition and BJP leader Suvendu Adhikari told reporters, "Whoever leaves the party it is his decision. But the party will seek their disqualification after asking them to explain their stand."