"I had written a letter to Sonia Gandhi about it, I had in fact resigned. But when I met her, she expressed regret and explained to me that it was a mix up. We talked about it and left it there. I have no hard feelings," Singh told PTI here on the sidelines of a symposium, 'Nehru and Today's India'.
His second-in command, Anand Sharma, along with Sonia and Congress Vice President Rahul Gandhi were part of the delegation which held an hour-long meeting with the US President.
Singh, however, did not reveal as to what explanation he was offered by the Congress president.
Meanwhile, rubbishing rumours that he was mulling joining BJP, he said, "I joined Congress half-a-century ago, the rumours might be because of my son who joined BJP recently, but my other son is in PDP... It's a democracy.