The news that longtime CBS entertainment chair Nina Tassler was stepping down may have been surprising, but not as much as the choice of her replacement — which sent a resounding, “Glenn Geller?” through Hollywood’s hallways.

Although Geller is a 15-year veteran of the Eye, his promotion — from an exec VP role overseeing current programming — was a surprise to the industry, given the deep bench of development executives at CBS’ network and studio, including Christina Davis and Julie McNamara.

“He’s got a steep learning curve,” an insider points out. “He’s not been a development exec. He’s got to learn the development game, chasing talent and all that stuff, as opposed to maintaining it. It’s a different challenge.”

CBS TV Studios boss David Stapf, who first hired Geller, says he’s not concerned about the new prez’s on-the-job training.

“A lot of the same skill set that is involved in being a good current executive is (involved) in development. I think the muscle that is less flexed is wooing and luring the talent in, but Glenn is extremely personable, very smart and is an artist’s executive,” Stapf says. “We joke that episode two is development.”

CBS CEO Leslie Moonves expressed full confidence in Geller, telling Variety that he was the clear choice for the job, thanks in part to his current programming expertise.

“It’s one of the most underappreciated areas at a network or studio,” Moonves said. “It’s the current execs who keep the schedule going. It’s where your strength lies. And Glenn has kept our schedule in solid shape through the years.”

Geller’s bosses point to the successful series on his resume: the long-running “NCIS” and “CSI” franchises, freshman breakout “Scorpion” and critical darling “Jane the Virgin,” plus “The Talk” and the new late-night wave of Corden and Colbert.

Stapf adds, “One of the things we’re very proud of is our return rate … That is in large part, not only due to the hard work of the writers, producers, actors, and crews, but also the current department that’s been led by Glenn forever. That sets him up really well to be the president of a network. He’s been in the trenches.”

“It makes sense. He has shepherded franchises into numerous seasons and awards,” an agent says, bringing up one of Geller’s most important assets: He’s schmoozed with the best. “When you’re in current, you’re holding and keeping relationships with showrunners and writers.”

Robert and Michelle King, creators of “The Good Wife,” have worked with Geller on their series since its launch. “He’s smart,” Robert says. “With Glenn, you really get a sense that the notes were truly about improving the project.”

Michelle, who says she often contacts Geller for advice, believes the new leader’s background in current will not be a problem. “My own perspective is, story is story. Whether you’re dealing with a story already on the air or one that hopes to be on the air, it’s the same muscle.” Her husband agrees: “When you’re a showrunner, you’re not sometimes distinguishing development and current. Glenn is someone who is smart and who can cross over.”

The showrunners both note that Geller periodically sends enthusiastic emails with words of praise for specific scripts or cuts he’s seen, “which is awfully nice because he’s not the executive directly responsible for ‘The Good Wife,'” Michelle says. “I get the sense that he reads every draft and watches every cut of the show. That’s a hell of a lot of work.”

Robert adds, “There’s sometime so anonymous about making these shows so to still get comments on them that are smart and complementary when we’re on episode No. 135 is very good for a showrunner.”

Geller says he knows he has his work cut out for him — but prides himself on his relationships with showrunners. “I have such a great respect for the writers who create our shows,” he says. “They are so passionate about every moment, every show, every script. I’ve learned how to work with talent and be respectful, but also how to get your point of view across. And I think I’ve been successful in that.”

Geller now has until the end of the year to train alongside Tassler, who will make her official exit as the year ends.

“I want to fill those shoes as best as I can,” Geller says of the longtime exec. “But I also have to be myself.”