Seemingly it wasn't just the once off either, apparently it was going on for approximately 3 years "right under her nose." And, as if that weren't enough, it was the family iPad that reportedly alerted The Voice star that the affair with the couples' nanny - Mindy Mann - was happening after 13 years of marriage. 

Us Weekly comes across with the following exclusive: "Back in February, Stefani, 46, uncovered Rossdale's long-term affair with Mann, who cared for the couple’s three sons, Kingston, 9, Zuma, 7, and Apollo, 20 months. At the time, the No Doubt frontwoman discovered explicit texts between Rossdale and the nanny - including nude photos of Mann and their plans to meet up for sex - on the family’s iPad."

Thankfully it wasn't Stefani or one of the kids who stumbled across the material on the "family iPad" rather another nanny who then alerted Gwen. Apparently the iPad was linked to Rossdale's phone. 

Initially, when Stefani found out, Rossdale claimed it was merely a "flirtation." But when he finally unburdened himself regarding the extent of the infidelity, Stefani decided to leave him, with the pair announcing their divorce in August. 

According to a source speaking to Us Weekly, the admission “completely devastated her. She was mortified, livid, and embarrassed. This was done right under Gwen’s nose." Given the affair spanned a reported 3 years, that means it was ongoing throughout her pregnancy with Apollo. 

Gwen has since announced her relationship with The Voice co-mentor Blake Shelton. We wish her every happiness.