Shari Redstone refused an offer from her media mogul father Sumner to sell her 20 percent stake in the holding company that controls Viacom Inc and CBS Corp for $1 billion, the Wall Street Journal reported.

The offer made in November 2014 would have required Shari to give up her right to become chairman of the two media companies upon the death of her father, now 92, the Journal reported, citing documents and people familiar with the matter.

The tax-free, cash-and-stock offer valued Shari's stake 33 percent more than its present worth, the Journal reported on Sunday. 

"It appears that third parties accessed and then disclosed to the Wall Street Journal highly confidential documents," Shari Redstone's spokeswoman Nancy Sterling said in an email, declining to comment further.

The report comes at a time when Sumner's physical and mental health have been the subject of intense debate, partly due to his notable absence from the companies' recent earnings calls.

Earlier this month, Viacom Chief Executive Philippe Dauman addressed these concerns, saying he speaks with Sumner several times a week and that the media mogul was in charge of his own health care.

In recent months Shari, 61, has made efforts to repair her strained relationship with Sumner, visiting him regularly and recently celebrating Hanukkah with him, the Journal report said.

CBS declined to comment on the report, while Viacom did not immediately respond to a request for comment.

Viacom has been posting weak revenue in recent quarters, as the MTV and Comedy Central owner struggles to boost ad sales in its U.S. cable TV business.

(Reporting by Sai Sachin R and Arathy S Nair in Bengaluru; Editing by Sriraj Kalluvila)