Media mogul Sumner Redstone has resigned as executive chairman of CBS and CEO Leslie Moonves has been appointed as his successor, the company announced on Wednesday. The resignation comes amid growing concern from shareholders regarding the 92-year-old billionaire's physical and mental competence.

"I am honored to accept the chairmanship of this great company," said Moonves, according to The Hollywood Reporter. "I want to thank Sumner for his guidance and strong support over all these years. It has meant the world to me." 

Redstone continues to serve as the chairman of Viacom and a board meeting has been scheduled for Thursday, where directors are expected to discuss his replacement, according to the Wall Street Journal.

Redstone, who controls about 80 percent of the voting shares in Viacom and CBS, is currently in the middle of a legal battle with former girlfriend and health care agent, Manuela Herzer, who filed papers in court challenging his mental capacity, according to Reuters.

Viacom revealed last month that Redstone's pay was cut by 85 percent as opposed to last year's amount owing to "reduced responsibilities."

Before appointing Moonves as the chairman, the board offered the position to Redstone's daughter Shari, but she turned it down.

"My father's trust states his intention that I succeed him as chair at CBS and Viacom, and also names me as a trustee after his death," Shari Redstone said on Wednesday. "However, it is my firm belief that whoever may succeed my father as chair at each company should be someone who is not a trustee of my father's trust or otherwise intertwined in Redstone family matters, but rather a leader with an independent voice."