Revealing this in his book 'The Coalition Years', Mukherjee said he had met Thackeray on the advice of Sharad Pawar of the NCP, a part of the Congress-led UPA-II government.
He said that during his campaign visit to Mumbai on July 13, 2012, he had gone to meet Thackeray at his residence after the Shiv Sena leader had extended his party's support to him despite being a part of the BJP-led National Democratic Alliance (NDA).
The veteran Congressman said he had asked both Gandhi and Pawar, who was instrumental in influencing Thackeray towards him, whether he should meet the Sena leader during his visit to Mumbai.
Pawar's advice was completely different from that of Gandhi as he insisted that Mukherjee should meet Thackeray.
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Pawar said Thackeray would consider it a personal insult if Mukherjee did not meet him during his visit to Mumbai.
After his return to Delhi, Mukherjee said, Congress leader Girija Vyas had met him and told him that Gandhi and Ahmed Patel, the political secretary to the Congress president, were upset about the meeting with Thackeray.
"I returned to Delhi, and the following morning Girija Vyas called on me. She informed me that Sonia Gandhi and Ahmed Patel were upset about my meeting with Thackeray. I understood the cause of their unhappiness but, as I have explained, I did what I believed was right. I had to keep in mind the sensitivity of the advice given by Sharad Pawar -- an important ally of the UPA-II," he said.
"Without the effective intervention and support of its partners, it would not be possible for it (the UPA) to complete the term. It was already known that Sharad Pawar was unhappy on various issues and the relationship amongst coalition partners was under stress. I did not want to give him further cause for unhappiness," he said.
Narrating his meeting with the Maratha strongman, the former president said it was "very cordial".
"He jokingly told me that it was but natural for the 'Maratha Tiger' to support the 'Royal Bengal Tiger'," Mukherjee said, adding that they also discussed some issues of internal security.
"I had known Thackeray as a politician with a sectarian approach, but at the same time, I could not ignore the fact that the man had gone out of the way to support my candidature," Mukherjee said.