A day after former External Affairs Minister K Natwar Singh sent his resignation to Congress President Sonia Gandhi, the ruling party expressed regret about his association with the party. “It was unfortunate,” said AICC media cell chairperson Veerappa Moily referring to Singh having been External Affairs Minister in the UPA Government. He said the Congress had to think of some internal disciplinary mechanism to “screen opportunists like him”. He said Singh’s resignation from the party was irrelevant as he had already been suspended by the party. Meawhile, Natwar called on Vice-President Mohammad Hamid Ansari on Thursday evening and submitted his resignation from the Rajya Sabha. His term is scheduled to get over in April even in the normal course. “The chapter is closed,” sources close to Natwar Singh said after his meeting with Ansari. According to official sources, the resignation letter is “under process” in the Rajya Sabha secretariat.