The Real Story! Inside Gavin Rossdale's Relationship With His Kids' Nanny & Why Gwen Stefani Couldn't Take It

Gwen Stefani and Gavin Rossdale weathered many storms in their 20-year relationship, but it only took one woman to break them apart for good. Multiple sources claim that the couple's nanny was at the center of their split, and only RadarOnline.com has the full story of what really happened.

According to a source, Stefani and the nanny, who cared for Kingston, 9, Zuma, 6, and Apollo, 17 months, "were very, very close."

"Gwen loaned her clothes, and was very generous with the younger woman," the source said. "The nanny was very attractive, but in the beginning, Gwen trusted her and treated her as a younger sister/best friend."

According to insiders, they were even known to dress alike! The woman was also a fixture on the set of The Voice and even accompanied the family on vacations.

But over time, "Gwen had suspicions that Gavin and the nanny had become romantically involved," the source revealed.

Both Rossdale and the woman strongly denied it, and there was no real evidence of any fling, but Stefani's rising suspicions eventually drove the nanny to leave the job and Los Angeles and move back East, according to multiple sources.

Said one source, "The constant stress and scrutiny just became unbearable for her."

However, a separate source insisted it was Stefani who pulled the plug. "Gwen absolutely fired the nanny," the source said. "She wasn't going to have this going on around the kids."

Meanwhile, "Gwen is absolutely devastated about the marriage ending, and she has been inconsolable," an insider previously told Radar. "But she had no other choice. She was very suspicious that Gavin was involved with the nanny."

"Gavin always denied anything inappropriate," the source continued, "but her friends warned her that it seemed like there was something going on."

For now, the couple is continuing to live under the same roof. "Gwen thinks he cheated, and they have been sleeping in separate bedrooms for months," the source explained, "so it really didn't make sense for Gavin to move out and upset the kids."