CBS Corp and Viacom Inc have reached an agreement in principle, sources familiar with the matter told Reuters on Tuesday, reuniting media mogul Sumner Redstone's U.S. entertainment empire after 13 years apart.

Viacom shareholders will receive 0.59625 CBS shares for each share they own, representing a slight discount to Viacom's closing price on Friday.

The two companies are controlled by National Amusements Inc, the holding company owned by billionaire Sumner Redstone and his daughter, Shari.

The deal represents a victory for Shari Redstone, president of National Amusement, after three attempts in as many years.

The recombination comes amid an increasingly competitive media landscape dominated by Walt Disney Co and Netflix Inc, prompting Redstone to pursue a merger.

CBS shareholders to get slight premium from Viacom deal -sources (Reporting by Kenneth Li and Helen Coster in New York and Supantha Mukherjee in Bengaluru; Editing by Saumyadeb Chakrabarty and Nick Zieminski) ((supantha.mukherjee@thomsonreuters.com; within U.S.+1 646 223 8780, outside U.S. +91 80 6749 6101; Reuters Messaging: supantha.mukherjee.thomsonreuters.com@reuters.net))