Following his summer move to Ibrox, Barton was revealed to have previously expressed affection for the Hoops in the form of tweets from years gone by.
Answering readers' questions in the October 2016 edition of FourFourTwo magazine – available now in print, on iPad and iPhone now – the 34-year-old insists he had never been a real fan of the side from Celtic Park.
"I don’t think I’ve ever supported Celtic," the midfielder told FFT. "I’m a born-and-bred Evertonian, I’ve not met any true football fan who supports two teams.
"My name is Joseph Anthony, I went to St Agnes Primary School and St Thomas Becket Secondary School, and my grandmother is a staunch Roman Catholic of Irish heritage. So when Rangers played Celtic, the same way as when Barcelona play Real Madrid, you pick a side based on what’s going on around you.
"Things like that are always an issue until the first game, then people know which side of the divide you stand on."
Barton is set to feature in his first Old Firm Derby on Saturday, when Rangers travel to Celtic Park for the Glasgow clubs' first league meeting since 2012.
Find out what else is in the latest edition of FourFourTwo
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‘He’ll still be playing at 40 at a good level because he’s in such good shape and looks after himself so well. He does everything to be a top professional’: Ex-Liverpool coach insists Mohamed Salah has plenty more miles in the tank
