Bo, sacked as the head of the Chongqing city last year following allegations of bribery, embezzlement and abuse of power against him, was facing trial in the Jinan Intermediate People's Court in eastern China.
The 64-year-old leader's wife Gu, who has been serving a suspended death sentence for murdering British businessman Neil Heywood, has become key witness for prosecutors in the bribery and embezzlement case against the disgraced leader.
Ironically for Bo, 54-year-old Gu's testimony against him in the cases made it difficult for him to refute the charges as she already acknowledged receiving money besides a luxury villa bought in France.
One of the charges against Bo was that he had "maintained improper sexual relationships", among other accusations. But details of his extramarital affair had not been included in the three charges brought against him.
Yesterday, Bo voluntarily told the court about his infidelity when he tried to discredit Gu's testimony that he knowingly let her accept five million yuan to improve the family's finances when she and their son Bo Guagua were living abroad.
"She would never complain about financial issues in front of me. She arranged the whole thing - to send Guagua to study at middle school in the UK - and took off after informing me," he said.
"She did this because I had an affair before and she was furious. She took Guagua away, to a large extent, to get back at me," he said without disclosing details of his affair.
Bo argued Gu's testimony was untrue as the family had no financial difficulties. Gu was a lawyer and her law firm was the most profitable in the country and she had opened five offices in Beijing, he said.
Bo said he remembered vividly the moment she broke the news to him, and how he felt she was being considerate in avoiding talk of conflicts of interest.
"It was something she did for me and was very proud of," Bo told the court.
