(CNN) - CBS Corporation is going through another big change -- but this one is entirely out of the company's control.
Richard Parsons is resigning from the company's board of directors just four weeks after becoming the interim chairman of the board.
"The reason for my departure relates to the state of my health," Parsons said in a statement shared by CBS.
"As some of you know, when I agreed to join the board and serve as the interim chair, I was already dealing with a serious health challenge -- multiple myeloma -- but I felt that the situation was manageable," Parsons said. "Unfortunately, unanticipated complications have created additional new challenges, and my doctors have advised that cutting back on my current commitments is essential to my overall recovery."
Board member Strauss Zelnick is the new interim chairman of the board. CBS said the changes take effect immediately.
"The appointment follows a unanimous decision this evening by the CBS Board," the company said.
While CBS (CBS) assets — such as its broadcast network and Showtime — are humming along, the corporation is in a period of wrenching change.
Longtime CBS CEO Les Moonves exited the company in September after two stories by The New Yorker's Ronan Farrow alleged incidents of sexual misconduct in his past. Moonves had been locked in a months-long corporate tug of war with controlling shareholder Shari Redstone.
Moonves called the misconduct allegations "untrue" and said the claims were coming up "as part of a concerted effort by others to destroy my name, my reputation, and my career," all but pointing the finger at controlling shareholder Shari Redstone. Her team rejected that suggestion.
Ever since Moonves resigned, Redstone has been consolidating control of the company. Board members close to Moonves have stepped aside, new representatives have joined, and the board has been dramatically reshaped. Parsons, for example, was brought aboard earlier this year at Redstone's urging.
Zelnick's arrival was another sign of the CBS board overhaul. He came aboard in early September at the same time Moonves resigned.
Zelnick has a big day job: He's the CEO and chairman of Take-Two Interactive Software, a leading video game publisher. He is also a former CEO of BMG Entertainment.
Parsons' tasks now transfer over to Zelnick. At the top of the list: Identifying a new CEO for CBS.
When Moonves exited, his longtime chief operating officer Joe Ianniello was named interim CEO. Ianniello has been rebuilding the executive ranks of CBS in recent weeks, but he is believed to be just one of the candidates for the permanent CEO job.
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