Sharad Pawar is at the receiving end of late Congress veteran Arjun Singh who has accused him of being flip-flop, unreliable and fickle and wondered when the "final rupture" would take place between him and the Congress.

Singh's criticism and his unfavourable assessment of the NCP chief has been made in the late leader's soon-to-be released autobiography "A Grain of Sand in the Hourglass of Time" being brought out by Hay House India.

The former Madhya Pradesh Chief Minister, who was Pawar's colleague in the Narasimha Rao cabinet and later, has attacked him for raising the foreign origin issue of Sonia Gandhi and his subsequent hobnobbing with Congress.

In the book, Singh has said that he had warned Rajiv Gandhi in 1986 against re-admission of Pawar in the Congress saying his "history was not at all inspiring" and he could again ditch the party any day.

"My assessment of Pawar's flip-flop nature proved correct in that, 13 years later, he began a malicious campaign against the leadership of the party. After being expelled, he formed a new party called the Nationalist Congress Party", he had written in the book.

Singh was also sure that this was not going to be the last act of Pawar, who, in one incarnation or the other, continues to hobnob with the Congress Party as a coalition partner.

"One is not sure when the final rupture would take place as it is bound to", Singh, who had been a Cabinet colleague of Pawar in the Narasimha Rao and UPA-I Government, said.