Lori Loughlin's Ex Mossimo Giannulli Always Felt She Was 'Too Flirty' With Costar John Stamos, Claims Insider: 'They Had Incredible Chemistry'

Did Lori Loughlin's close relationship with John Stamos play a part in her separation from Mossimo Giannulli?

While rumors swirled Giannulli was the one causing issues in their marriage, an insider claimed he always found the Full House costars' dynamic "too flirty for comfort."

"They’ve always had incredible chemistry," the insider spilled to Rob Shuter's Substack. "But Mossimo never believed it was just acting. He thought John’s charm didn’t stop when the cameras did."

The insider alleged that Giannulli, 62, despised seeing Stamos, also 62, at red carpet events or Hollywood galas.

"Lori would light up when John walked in. Mossimo would shut down," the source claimed. "He saw John as competition — not Uncle Jesse."

While the mom-of-two, 61, was thankful Stamos supported her through the estranged couple's college admissions scandal, Giannulli wasn't so thrilled.

"Mossimo didn’t see that as friendship," the source noted. "He saw it as crossing a line."

The musician has been married to Caitlin McHugh, 39, since 2018.

Oddly enough, Stamos was asked about his friendship with Loughlin when he appeared on the October 20 episode of the "Good Guys" podcast.

After Loughlin's split was mentioned, co-host Ben Soffer explained that fans’ biggest question for the actor was about "bringing Aunt Becky... into the fold" of his marriage.

"Like a threesome?" the dad-of-one asked. "No."

The host then clarified the question, saying, "They didn’t ask that. They asked, ‘Would you leave your wife for her?’ We’re not doing that."

"No f------ way," he declared.

Stamos explained there was a "very small" amount of time when he and Loughlin were both single.

“I don’t mean to belittle or pare it down to Grease, but Lori was Sandy, you know before the leather and all that stuff, before that song. Rebecca Romijn was Sandy in the leather and the, ‘Tell me about it, stud,’" he said, mentioning his ex-wife. "There was a moment where I had the choice, I think. And I was more into, you know, the rebellious. Lori was sweet and I loved working with her, but she was too nice for me."

As OK! reported, Giannulli and his estranged wife's separation was revealed on October 2 after 28 years as spouses.

"They are living apart and taking a break from their marriage," Loughlin's representative Elizabeth Much said in a statement. "There are no legal proceedings at this time."

Sources claimed the two had trust issues for years, with a pal of the actress' alleging Loughlin made the decision to separate after she recently found "incriminating" texts and emails on Giannulli's phone.

While the Hallmark star is "devastated" by the ways things unfolded, a source told one publication, "They will not reconcile — there is currently no chance — and will ultimately divorce."