Thiruvananthapuram | Manmohan Singh was the most humble prime minister India has ever seen, says T K A Nair, who was his principal secretary during the UPA rule.

Speaking to a television channel, Nair, the former IAS officer who is currently settled in Thiruvananthapuram, said on Friday that despite facing intense criticism throughout his tenure, Singh remained steadfast in fulfilling his responsibilities.

"Even when political opponents labelled him a ‘dummy' or ‘shadow PM,' he remained focused on serving the country's best interests," Nair said.

Singh refrained from making personal attacks against his critics and rivals, he added.

Responding to the reports during Singh's tenure suggesting that a section of Congress leaders did not fully support him or certain decisions made by his government, Nair said: "I could sense the severe mental pain he was enduring, but he never let it show.

"He neither acted against nor voiced opposition to his party's leadership," Nair said, stating Singh's unwavering loyalty to the party line and leadership.

After completing his 10 years as prime minister, Singh expressed a sense of satisfaction, confident that he had sincerely served during his term, he recalled.

"He inspired his colleagues through his work," said Nair, who worked closely with Singh for both his terms.

Singh was a prime minister who made time for everyone -- whether cabinet colleagues or officials -- greeting them warmly, interacting with them, and always ensuring they left on a cordial note, Nair recalled.

Singh, the architect of India's economic reforms, died at AIIMS, New Delhi on Thursday. He was 92.