Britain-based brewer SABMiller said on Tuesday that its chief executive Graham Mackay has had surgery for a brain tumour and would be replaced by the group's chief operating officer.
"He underwent surgery yesterday, 22 April 2013, and will now embark on a course of treatment," the company said in a statement to the London Stock Exchange.
"Accordingly, the board has accelerated the planned promotion of Chief Operating Officer Alan Clark to chief executive with immediate effect.
"Mr Clark was appointed as chief operating officer in July 2012 with a view to succeeding Mr Mackay as chief executive in July 2013 after a transitional period of one year, when it was intended that Mr Mackay would become non-executive chairman."
In a note to SABMiller employees, Mackay said: "I am inexpressibly proud of this company, what it has achieved and the shape it is in.
"I certainly do not expect there to be any impact from this development on its operations or strategic direction, which will continue to run as normal."
He added: "I obviously have an additional personal objective, and that is to get well as quickly as possible for the sake of my wife and children. Thank you all for your support."
The news comes less than a week after SABMiller announced that its revenues jumped higher in the group's 2012/2013 financial year, lifted by particularly strong demand in India.
Group revenues rose 7.0 percent in the 12 months to the end of March on a constant currency basis, SABMiller had said in a trading update.
SABMiller, which purchased Australian beer giant Foster's in 2011, said that its overall financial performance was in line with expectations.
The maker of Grolsch and Miller Lite also revealed that annual lager volumes rose by 3.0 percent.
Volumes surged by a hefty 20 percent in India, and by 5.0 percent in China.
In Europe, SABMiller added that volumes were up 6.0 percent despite the challenging economic backdrop.
SABMiller, which is listed in London and Johannesburg, produces other well-known beer brands including Peroni Nastro Azzuro and Pilsner Urquell.