Longtime CBS executive Nina Tassler announced in a press release that she was leaving the network after 18 years. Tassler was the chairman of the network and said she would step down from her position at the end of the year. In the announcement she said she would also stay with the company in an advisory role though at least 2017.

Tassler ran CBS Entertainment since 2004 and was with the company since 1997. Since June 2013 she served as executive vice president of Current Programming for the CBS Entertainment Group, where she oversaw the company's network and studio department as well as the creative affairs for more than 30 primetime series on CBS and The CW.

Glenn Geller, the head of Current Programming for both CBS Entertainment and CBS Television Studios, was announced as the new president of CBS Entertainment. He has been with CBS since 2001.

"CBS is a special place," Tassler said. "For the past 18 years, I've been blessed to be part of an amazing team that has lifted this network to an enviable run of success.

"I will always love this place, yet it is time for my next chapter, and I'm thrilled that I can pursue my other creative interests while still being part of the company. I pass the baton to Glenn with great confidence and pride. He is an outstanding leader with great respect for the artistic process and a clear vision for programming success," she finished.

Thanks to Tassler's vision, CBS was the No. 1 network for 12 of the past 13 years. She was responsible for an incredible number of hit television shows that includes "NCIS," "The Big Bang Theory," "The Good Wife," "Criminal Minds" and "How I Met Your Mother."

She also led the network's late-night transitions with "The Late Show with Stephen Colbert" and "The Late Late Show with James Corden."