Billionaire Carlos Slim will buy out AT&T Inc.’s $5.9 billion stake in America Movil SAB, keeping the Latin American mobile-phone company’s outstanding shares from being diluted as the U.S. company exits the business.

Slim’s holding company, Inmobiliaria Carso, told America Movil’s board it will acquire AT&T’s 8.3 percent stake, which includes 24 percent of the company’s voting shares, according to a filing today. America Movil didn’t say how much Carso would pay.

AT&T is selling its holdings of Slim’s company after a 24-year relationship to avoid a conflict of interest because the Dallas-based company is buying DirecTV, which competes with America Movil for pay-TV customers across Latin America.

America Movil shares rose as much as 6.5 percent to 13.66 pesos in Mexico City. If AT&T had sold the stake in the open market, it could have reduced the value of America Movil shares by making them less scarce.

“America Movil recognizes the great value that the AT&T partnership produced for both parties in these more than 20 years,” Slim’s company said.