PEOPLE has learned that Flipping Out star Jeff Lewis is no longer working with longtime collaborator and friend Jenni Pulos

Jeff Lewis has been known to fire an employee or two on Flipping Out. But the latest shakeup might be the saddest for fans of the Bravo show.

PEOPLE has learned that Lewis is no longer working with longtime collaborator and friend Jenni Pulos.

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According to multiple sources, Pulos parted ways with Jeff Lewis Design — the house flipper’s company — a few months ago. The emotional moment is said to have been filmed for the upcoming eleventh season of Flipping Out, which premieres September 11.

Since then, the two haven’t spoken at all. “It’s sad,” one source says. “They used to be inseparable but their differences just got too big to overcome.”

“They found fame together so there was always this thought that nothing could tear them apart, but that hasn’t been the case,” the source adds. “They’ll never come back from this. It’s over.”

Image zoom Jenni Pulos and Jeff Lewis Isabella Vosmikova/NBC/Getty Images

Reps for Lewis, 48, and Pulos, 45, as well as Bravo did not respond to PEOPLE’s request for comment, but tensions between the pair — who have been friends for over 20 years — had been mounting for months, a second insider explains.

“It was a combination of things,” the second source explains. “They both had different priorities pushing them in opposite directions. … It was only a matter of time before it eventually exploded.”

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Pulos had gone on maternity leave from Jeff Lewis Design after the birth of her second child Georgia Grace, 1, and had returned to find many of the responsibilities of her position redistributed, the source says. While Lewis promoted Pulos to a new position, she felt like she wasn’t being given the opportunities to advance that she wanted. “She felt entitled to more than Lewis could give her,” the source says.

At the same time, Lewis’ patience with Pulos had been running thin, the insider explained. “Jenni was Jeff’s longest employee,” the source says. “He thought of her as his No. 2, but she wasn’t invested in the same way he was.”

Image zoom Jeff Lewis and Jenni Pulos David Livingston/Getty Images

While many different things factored in to their feud, there was one blowup that led to the end of their friendship, a third source tells PEOPLE.

“It was a horrible fight that was uncomfortable for everyone around them to watch,” the source says. “There were too many hurt feelings there and they both just unleashed on one another.”

With Lewis and Pulos at odds, the future of her appearances on additional seasons of Bravo’s Flipping Out remains to be seen.

Though the show follows Lewis and his employees, Pulos as played an integral role since it debuted in July 2007. Like Lewis, she’s also an executive producer on the series.