Gwen Threatens Gavin: You Had An Affair With The Nanny & I Have Proof!

Gwen Stefani doesn't care if people think she moved on from her marriage too soon, because RadarOnline.com has learned she believes Gavin Rossdale had a relationship with one of their nannies for several years — and she's telling friends she has proof!

According to an insider, Stefani's fears about her marriage got another jolt the day after the Grammy Awards this winter, when she was approached by household staff members who claimed they believed Rossdale was getting too close to the family nanny.

According to the source, the staff told Stefani "there were several times that Gavin was caught hanging out with the nanny when the kids weren't around. They were extremely flirty with each other, and would go for long drives, alone. There were text messages that Gwen also found on Gavin's phone that she thought were very incriminating."

"Gwen had been very suspicious about the nanny and Gavin, but he always denied anything inappropriate was going on," the source said. "The day after the Grammys was when the staff confronted Gwen with their allegations and it all blew up. Gavin continued to deny it at first, but finally confessed he had been seeing the woman away from the kids. There was no way to deny it any further. The nanny had worked for the family for two years."

"The relationship between Gavin and the nanny eventually ended," the source said, "but by then, it was just to late to save the marriage. Gwen had had enough."

RadarOnline.com has chosen not to reveal the identity of the nanny, a younger look-alike of Stefani.

Stefani recently hinted at this incident during an emotional interview with Ryan Seacrest. The Voice judge said, "My life blew up in my face," the day after the 2015 Grammys, adding, "And now I'm in this new life, and it's pretty awesome I have to say -- I'm so inspired and being back on the show, and just being in a new place. Everything just feels new. I just feel inspired. I don't know how else to describe it."

The source said Rossdale is still in contact with the former nanny, but "only to check in on her and how she is doing."

"This has been very confusing and troubling for the kids," the source claimed. "They loved the nanny and don't know why she was let go. Everything Gwen does is for those boys. She is a great mom."

Reps for Rossdale didn't immediately respond to RadarOnline.com's request for comment, and the former nanny for the family did not either.