Saudi tycoon Prince Alwalid bin Talal has severed his ties with Forbes magazine\'s annual billionaires\' list, which he accused of undervaluing his fortune, his office said Tuesday. In its 2013 list published on Monday, Forbes ranked Alwalid 26th in the world with a fortune it estimated at $20 billion (15.4 billion euros). The prince\'s office and his Kingdom Holding investment group \"have ended their long-standing relationship with the Forbes Billionaires List,\" a statement said. Alwaleed wrote to Steve Forbes, the magazines\'s chief editor and chairman, \"requesting that the prince be removed from the list and informing Forbes\" that officials from Kingdom Holding would no longer work with its valuation teams. The statement accused Forbes of \"intentional biases and inconsistencies\" in its valuation process over the past six years as it refused to accept share values as listed by the the kingdom\'s stock exchange, Tadawul. \"Prince Alwaleed has taken this step as he felt he could no longer participate in a process which resulted in the use of incorrect data and seemed designed to disadvantage Middle Eastern investors and institutions,\" it added. Forbes team has considered \"rumors that stock manipulation \'is the national sport\' in Saudi Arabia because \'there are no casinos\'\" in the ultra-conservative kingdom during their valuation process, it said. But Kingdom Holding will continue to cooperate with the Bloomberg Billionaires valuation teams, which Alwalid \"considers to use a more accurate method of calculating financial holdings.\" Bloomberg Billionaires calculated the wealth of Alwalid, a nephew of King Abdullah, as $28 billion. The prince, in his late 50s, has holdings in Citibank and Rupert Murdoch\'s News Corp. Forbes magazine listed him last year as the 26th richest person in the world with assets of $19.6 billion. Kingdom Holding, of which he owns 95 percent, has stakes in Four Seasons and Fairmont Raffles Hotels International. In December 2011, Prince Alwalid and Kingdom Holding announced a combined investment of $300 million in the social networking site Twitter.