Pharma billionaire Stewart Rahr’s divorce payout to Carol, his wife of 43 years, could be as much as $800 million, sources say. The flamboyant party-loving playboy Rahr, who sold his pharmaceutical business Kinray in 2010 for $1.3 billion, never signed a prenuptial agreement with Carol. A source told us, “Stewart always said he’d never get divorced because it would be too expensive. They met when he didn’t have two cents to rub together. She could be entitled to half his $1.6 billion fortune.” Page Six exclusively revealed Carol, who has two adult children with self-titled “Stewie Rah Rah — the king of all fun,” served him with divorce papers late last week. A source said, “Stewart was served with the papers right outside his Park Avenue apartment building. He was furious it was done in such a public way.” Another source told us Rahr’s recent epic fit at Nobu Fifty-Seven, when he cursed out a manager over arrangements for Carol’s surprise birthday, finally forced his wife to seek a divorce lawyer — and she went for the “pit bull” of divorce lawyers Robert Stephan Cohen. The source said, “Carol was so embarrassed that he created a war over her birthday.” Of Rahr’s penchant for surrounding himself with young attractive women at parties, “Carol always knew what was going on, but recently he seems even more out there and generous with his money. He went out and bought 12 Teslas to give away to his friends, he gave $7 million for prostate cancer research. She fears Stewart is so out of control he could give away all his money, half of which is hers.” Her attorney Cohen wasn’t reachable last night, but Rahr’s lawyer Ben Brafman said, “Virtually all of the money Mr. Rahr has given away in recent years has gone to wonderful charitable organizations that are using those funds to save lives and help find a cure for cancer.”