Saying that he was saddened at the position taken by Singh against the Congress President, Khurshid also criticised his former colleague for forgetting that a person accepted as a leader in good times needs to remain so in bad times too.
The latest book titled 'One Life is Not Enough' by Singh, who is also known as a mentor of Khurshid and both of them have served in External Affairs Ministry during Congress-led governments, has created an intense political debate, especially on issues related to Sonia Gandhi not taking up the Prime Ministerial position after 2004 general elections.
An estranged Gandhi family friend, Singh had to resign from the UPA-I Government in 2005 in the wake of the Iraqi oil-for-food scam. Later, he also quit the Congress party.
"We have benefited enormously from his (Natwar Singh's) guidance in the past. I am very saddened that somebody who gave us good counsel and guidance should himself have forgotten that," Khurshid told PTI in an interview here.
"It saddens me greatly and on this occasion I say that all of us have, I think, enormous gratitude to Congress leadership, Congress President Sonia Gandhi. When you accept someone as your leader, it can't be only for good times, it has to be for good times and bad times.
"It can't be only when you are getting something and you have to give something. After such a long and distinguished service, Natwar Singh was persuaded to take this position.
"I am really very, very saddened and I think this is something on which we should move ahead very quickly and forget that this has happened because it leaves a very, very unpleasant taste in the mouth," said Khurshid, who was here to attend a power sector conference organised by the Independent Power Producers Association of India (IPPAI).
Responding to a query on Singh who said that Sonia Gandhi declined prime ministership on the advice of Rahul Gandhi, Khurshid said he was not privy to all the discussions.
"We can only go by what we have heard from Sonia Gandhi, what she said publicly. That is something we have repeated many times and we have respected her for it. Within confines of a family discussion, there can be many many factors that could be discussed but ultimately you can only accept what your leader says about her main motivation.
"Her main motivation at that time was that she felt that something came from within her that for national reconciliation and taking the country forward, it was time for her not to accept (the prime ministership). We have to respect what she said and I don't think it is a pleasant thing that if there was any discussion that someone was privy to that should be brought out in the public," the former minister noted.