The result is “Extended Family,” which premieres on NBC on Saturday night (8 p.m. EST, following the football) starring Jon Cryer (“Two and a Half Men”), Donald Faison (“Scrubs”) and Abigail Spencer (“Grey’s Anatomy,” “Suits”) in a love triangle inspired by the real-life dynamic that developed between Grousbeck, his new wife and her ex-husband — a lifelong Celtics fan.

“He looked at her like: ‘There’s a million guys in New England you could be dating,’” said Werner, who advised the three on developing the show and joined them as an executive producer. “What am I going to tell my friends?”

The ensuing hijinks play off the decision by Emilia Fazzalari and George Geyer to follow their divorce with an arrangement called nesting: Instead of making the children bounce around during custody swaps, the kids stay in the family apartment and the parents move in and out.

“The nest is someplace where Julia and I have tried to give our kids the false impression that nothing has changed,” Jim Kearney (Cryer) says in the pilot, which revolves around a true story in which Geyer was left in charge of his daughter’s goldfish “Googles” while she was at summer camp. The fish dies, they decide to replace it with a look-alike, and then wackiness ensues.

Fazzalari and Geyer said the unusually amicable divorce was an attempt to minimize the disruption for their two children.

“We decided to get divorced, and we decided that we should pay the price for that, not the kids,” Geyer said in a recent interview. “You can choose two routes when you get divorced. You can choose to be horrible or you can make the best of it. And we chose to make the best of it.”

And everything was fine — until Fazzalari started dating Grousbeck.

In the pilot, Jim hits Celtics owner Trey Turner (Faison) up for tickets and his ex-wife Julia Mariano (Spencer) says: “Looks like we both met the man of our dreams.” But in real life there were more mixed emotions for Geyer, who grew up outside of Boston, went to Boston College and raised his kids as Boston sports fans while living in New York.

“It has to sting, right?” he said. “I’m a Celtics fan and she starts dating the owner of the Celtics? Not to mention being Irish and growing up in Boston and having all my Boston friends — you know how they like to give people a hard time. You can imagine the grief I’ve taken from them as far as my wife being now married to the owner of the Boston Celtics.”

On a recent Zoom call, Grousbeck, Fazzalari and Geyer banter good-naturedly, just as the characters do. When Geyer refers to Fazzalari as his wife, she corrects him: “ex-wife”; Geyer gives Grousbeck a hard time about the trade of NBA championship-winning point guard Rajon Rondo.

“It’s not a documentary,” Geyer said. “But if you watch the way the three characters interact on screen, it is pretty similar.”

And though there are some ideas taken from their lives, most of the stories are created in the writers’ room, where Geyer, who is mostly retired after working 30 years for Bloomberg LLP, sits in two weeks a month as a contributor. “I even have gotten one or two lines into the show,” he said.

Werner said he is often approached by people who think they have good ideas for a TV show, much like Red Sox fans make lineup suggestions. (“It’s kind of like when someone says, ‘Why didn’t you take that pitcher out in the seventh inning?’” he said. “Everyone thinks they’re smarter than the manager.”)

But he was sold on the premise for “Extended Family” when he was on vacation in Mexico with Grousbeck and Fazzalari and he overheard her talking — and laughing — to Geyer on the phone.

“I hang up and Tom goes, ‘I thought you were going to have a conversation with your ex-husband.’ I go, ‘No, that was my ex-husband,’” Fazzalari said. “Wyc at that point said, ‘Let me tell you about this interesting situation. I actually think it’s a sitcom.’”

Werner sent them some past treatments as examples, and then gave them notes on their effort. Grousbeck and Fazzalari — who also created tequila company Cincoro with NBA great Michael Jordan — and Geyer are executive producers of the show and involved in the casting, set design, costumes and scripts.

Veteran actor and writer — and fervent Boston sports fan — Mike O’Malley was brought on as the showrunner and creator.

“When they call you to do something like this, you’re excited because you think you might get some good tickets,” said O’Malley, who also worked with Werner — and NBA star LeBron James — on the series “Survivor’s Remorse.” “But then you realize: If I blow this, I might be persona non grata.’”

Comedian Lenny Clarke brings his authentic Boston accent to his part as Jim’s father. Former Celtic — and Laker — Rick Fox, who has a few dozen acting credits, plays the team’s general manager. The show, which has been picked up for 13 episodes, is scheduled to move into a regular timeslot on Tuesday nights at 8:30 p.m. EST starting Jan. 2.

One way “Extended Family” does keep it real: It uses the Celtics name and other actual NBA intellectual property. There is an external shot of the TD Garden, where the Celtics play, and a scene that takes place in a luxury suite festooned with framed jerseys — the No. 00 of Robert Parish, the No. 20 of Ray Allen, and the No. 41 of … Kelly Olynyk?

“The show wasn’t going to be the same if it was the Boston Bluebirds,” Grousbeck said. “The NBA said: ‘Go for it.’”

The pilot was shot during the 2022 NBA Finals, when Grousbeck and Fazzalari happened to be spending some time in California to watch the Celtics play (and ultimately lose to) the Golden State Warriors.

“It was amazing for the three of us to sit there and look at three people playing versions of us, loose versions of us,” Grousbeck said. “It’s like you’ve suddenly gone into the television. I mean, it’s just a crazy feeling.”