Canberra - Australia's prime minister confirmed on Friday that his predecessor and intra-party rival Tony Abbott had once been too drunk to vote in Parliament, an incident that's been a poorly kept secret in political circles for eight years.Prime Minister Malcolm Turnbull told Melbourne Radio 3AW on Friday that he was opposition leader in 2009 when Abbott was incapable of voting against government legislation to massively increase economic stimulus spending.Abbott replaced Turnbull as leader of the conservative Liberal Party late in 2009 and became prime minister before Turnbull ousted Abbott in a party ballot in 2015."I was disappointed, but you've got to move on with these things," Turnbull told Melbourne Radio 3AW of Abbott's inebriation."I can't remember anyone else missing a vote because they were too drunk to get into the chamber," he added.Confession Turnbull told the truth over the episode after media reported that Abbott had finally confessed in a television interview that will be screened on September 5.Abbott said he had gone to sleep on his office couch after he'd been drinking wine with two party colleagues."The impact was rather greater than it should have been," the Herald Sun newspaper quoted him as saying."I lay down, and the next thing knew it was morning," he added.Turnbull said party officials responsible for making sure lawmakers were available for votes, known as whips, could not wake Abbott."There was nothing we could do," Turnbull said."The whips tried to rouse him to get him down into the chamber to vote but they were unable to move him," he added.'Impertinent'Turnbull said the need for lawmakers to attend every vote was now even greater, since the ruling coalition has a single-seat majority in the House of Representatives, where parties need a majority to govern.Abbott previously said he had missed the vote because he was tired after days of working as a volunteer firefighter. He dismissed a journalist's question of whether he had been drunk as "impertinent."Abbott remains a government lawmaker and retains strong support from his party's hard-right faction. He has become a vocal critic of the Turnbull administration's policy direction, as the government lags behind the centre-left opposition Labour Party in successive opinion polls.Abbott and Turnbull are now on opposite sides of Australia's gay marriage debate. Abbott is campaigning against same-sex marriage ahead of a national postal survey on the subject next month, while Turnbull supports marriage equality.Abbott did not immediately respond to a request for comment on Friday.