Richard Plepler. Photo: Daniel Zuchnik/Getty Images

HBO CEO Richard Plepler, the well-connected and equally well-respected TV executive who’s helped run the premium network since 2007 and green-lit Game of Thrones, is stepping down. In a letter to staffers late Thursday, Plepler described the decision as his own: “Hard as it is to think about leaving the company I love, and the people I love in it, it is the right time for me to do so,” he wrote. Still, Plepler’s resignation comes amid reports that former NBC and Showtime chief Robert Greenblatt is in line for a top job at HBO parent WarnerMedia, a position which would have made Greenblatt Plepler’s boss. As one industry veteran told Vulture hours before news of Plepler’s resignation hit, “I can’t see a scenario where Richard stays if he reports to Bob.” While there’s no official word yet that Greenblatt is, in fact, headed to WarnerMedia, it seems that even the possibility of a shake-up at WarnerMedia was enough to prompt Plepler to depart.

At the heart of today’s news is tension between Plepler and John Stankey, the CEO of HBO parent WarnerMedia. Stankey, a longtime telephone company executive, gained oversight of WarnerMedia (and thus HBO) when AT&T took control of the now-defunct Time Warner last year. Stankey and AT&T have made it clear they expect HBO to lead the charge in helping WarnerMedia build its own Netflix-style streaming offering, one in which mass amounts of programming are seen as key to driving growth — as opposed to the more curated approach which has served HBO for decades (and made it the crown jewel of WarnerMedia.) One top agent tells Vulture he believes today’s news became almost a foregone conclusion as long ago as last summer, when Stankey appeared at a town hall with HBO employees and talked up the need for HBO to make more shows and make (even more) money. “The first shoe came down last summer during the town hall,” the agent says. “The other shoe just dropped. This was inevitable.”

While that town hall sent shock waves through the halls of HBO’s New York and L.A. offices, a few weeks later, Stankey claimed his comments had been misinterpreted. And some HBO insiders Vulture spoke to at the time suggested they thought Stankey and his bosses at AT&T would ultimately be respectful of HBO’s unique culture and not risk making major changes. There was a growing acceptance that HBO would be doing more shows, and some insiders even considered this a good thing — noting a lack of money had sometimes kept HBO from competing for big projects it really wanted. But as one industry insider familiar with the thinking of AT&T execs told Vulture today, “You don’t pay $85 billion for a company and not try to put your stamp on it.” Indeed, in his letter to HBO staff, Plepler seems to hint that changes are in store for the network, saying he made his decision at “what is an inflection point in the life of this wonderful company.”

A source inside HBO says Plepler informed Stankey he planned to move on a few weeks ago, before reports of Greenblatt heading to WarnerMedia went public. However, there had been buzz about tension between Plepler and Stankey for months, so it’s not far-fetched to think Stankey informed Plepler of plans to change strategy or shake-up WarnerMedia’s corporate structure— and Plepler then decided to leave. A WarnerMedia rep declined to comment on reports of a bigger exec restructuring at the company or of the possibility of Greenblatt coming onboard. Stankey, however, issued a statement praising Plepler. “Richard is one of the most successful executives in our industry and I have been fortunate to have his support over the last months,” he said. “His vision, energy and passion helped to elevate HBO’s brand to what it has become today.”

Plepler joined HBO in 1992, originally overseeing communications and PR for the company. In 2007, he moved into programming and was named co-president of the network; he was promoted to CEO of Home Box Office Inc. in 2013. In addition to GOT, Plepler played a role in ordering series such as Veep, Girls, Boardwalk Empire, True Blood, Big Little Lies, Westworld, and Last Week Tonight With John Oliver. He also led HBO into the digital age with the successful rollout of HBO Now, and has grown the company’s overall global subscriber count by 40 percent over six years, to 140 million. He’s helped achieve similar growth in revenue, boosting HBO’s income to $6.6 billion. There’s no word yet on exactly when Plepler will depart HBO, though one insider expects he’ll stick around for several weeks to guide a transition. Here is the full text of Plepler’s letter to staff:

My dad always gave the best advice. Whenever there was a difficult decision to make, he counseled that since no one could ever have perfect visibility into the future, the best thing you could do was trust your instincts. It has been a touchstone for me throughout my life, and I have found myself returning to it again recently as I think about what is an inflection point in the life of this wonderful company. Hard as it is to think about leaving the company I love, and the people I love in it, it is the right time for me to do so. In the past weeks, I’ve thought a lot about the incredible journey of this company in the nearly 28 years that I have been blessed to be here. It’s a journey of great pride and accomplishment because so many of you, and many others before us, have made HBO a cultural and business phenomenon. Thanks to all of you, we are today churning on all cylinders both creatively and as a business. Thanks to all of you, I can move on to the next chapter of my life knowing that the best team in the industry remains here to carry on our continued progress and success. As I have said before, this is the team of teams. It has been the great joy of my professional life to share this ride with you over these many years. And the great honor of my professional life to be your CEO. I don’t have the words to express my gratitude for the support and talent that made our success together possible. But suffice it to say, my love for this place, and for all of you, is deeply a part of me and will last a lifetime. I look forward over the coming weeks to thanking as many of you as I can for the thousands of contributions big and small that have made “this thing of ours,” to quote Tony Soprano, so special. I have told John, who has been nothing but gracious since we spoke, that I would work closely with him to assure a seamless and organic transition. We’ve created a great and unique enterprise and I know that you will protect its legacy and do all to enhance its future in the years to come. Know that I will always be cheering loudly, even when I am outside this building, as HBO continues to thrive. With respect, admiration, and gratitude, Richard