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At least he's got a sense of humor!

Presidential hopeful Rick Perry had a major brain freeze at Wednesday's GOP debate in Detroit when he couldn't remember one of the three government agencies he said he wanted to cut. But on Thursday, the 61-year-old Republican poked fun at his error -- and even jokingly blamed Justin Bieber for the gaffe!

The Texas governor appeared on The Late Show with David Letterman and delivered the Top Ten List of "Rick Perry Excuses."

"I just learned Justin Bieber is my father!" he joked. (Bieber, 17, recently agreed to take a paternity test to disprove claims that he's the father of Mariah Yeater's 3-month-old son.)

More reasons why Perry wasn't exactly well-versed on Wednesday? "I was up late last night watching Dancing with the Stars," he quipped. "You try concentrating with Mitt Romney smiling at you. That is one handsome dude."