EXCLUSIVE, Updated with Viacom’s announcement: Viacom is making a change at the top of Comedy Central following months of declining ratings. President Michele Ganeless is stepping down at the end of this month after a 12-year tenure and a 25-year run at the company, to be replaced by top lieutenant Kent Alterman, currently president of original programming. The company announced the executive shakeup after Deadline broke the news.

Ganeless, who recently oversaw the network’s late-night transition post-Jon Stewart and Stephen Colbert, will remain at the company as a consultant through September. She says that “the time is right to move on and challenge myself in new ways.”

Alterman will be based in Santa Monica, and report to Doug Herzog, president of Viacom Media Networks Music & Entertainment Group. David Bernath will become Comedy Central’s General Manager, reporting to Alterman. Read below the story Herzog and Ganeless’ memos about the change.

Herzog praised Alterman’s “extraordinary talent for uncovering and elevating original comedic voices who bring a distinct point of view to the table. Finding and nurturing great talent is what we do best, and we are doubling down on that approach.”

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CEO Philippe Dauman promised analysts last month that revivals at Comedy Central as well as MTV “will be a driver of our advertising revenue recovery as we head into our next fiscal year.”

Herzog already made a top executive change at MTV with the hire of Sean Atkins as president in September. Last week, Atkins brought in longtime Major League Baseball chief marketing officer Jacqueline Parkes as EVP of Marketing and Creative, and Lifetime’s SVP and head of non-scripted Eli Lehrer as EVP overseeing MTV2.

Alterman was head of New York development at Comedy Central from 1996 to 2000, and rejoined in 2010 after stints working with Fox Film Studios and New Line.

He has been on the rise since. Promoted from EVP to President, Content Development & Original Programming in 2013, Alterman, based in Santa Monica and reporting to Ganeless, has overseen the development and day-to-day operations of all original programming on Comedy Central’s linear channel and digital platform. Known for his trademark deadpan quotes in press announcements, Alterman has been involved in the development of The Daily Show with Trevor Noah and The Nightly Show with Larry Wilmore as well as Inside Amy Schumer, Broad City, Key & Peele, Drunk History, and Not Safe with Nikki Glaser.

In their internal memos, Herzog and Ganeless noted that the news of the changeover was supposed to be unveiled tomorrow, with the announced moved up because of Deadline’s story breaking the news.

Here is Herzog’s email, followed by Ganeless’ farewell to her colleagues.