Ian Bailey, the English journalist who is suing seven newspapers for libel, wrote in 1993 that he had tried to kill his partner, Jules Thomas.
Mr Bailey, who is suing the papers over their coverage of the Sophie Toscan du Plantier murder, said in Cork Circuit Court today that he could not explain this entry in his diary.
He admitted under cross-examination he had forgotten that he had been so frank with himself.
Mr Bailey had pleaded guilty to assaulting Miss Thomas in August 2001 and received a suspended sentence. In court this morning, he said he could not recall Miss Thomas's injuries, but accepted he was responsible for them.
He accepted that he had inflicted injuries to her face and body. He also accepted after repeated questioning that he had probably hit Miss Thomas during an incident in Cork City in 1993. Miss Thomas later required hospital treatment.