Emily Maynard Cheated on Jef Holm With Matt Leinart

Emily Maynard's mysterious other man has finally been revealed.

As the Aug. 22 issue of Us Weekly reported, Bachelorette's Emily Maynard was caught exchanging explicit text messages with another, unidentified man -- leading to an explosive fight with fiance Jef Holm during a family vacation in South Carolina.

The texter on the other end? Hunky Oakland Raiders quarterback Matt Leinart, 29, a source confirms in the latest issue of Us Weekly, out now.

Indeed, Holm had a heart-to-heart with ex Kaylee Shepherd about the incident. "He said the story was 100 percent accurate," Shepherd, 21, tells Us. "When she put her phone down, [Jef] picked it up and read through everything. . . Jef said, 'It was that pro football guy . . . She strung me along and was talking to another guy the whole time!'"

Still, as fans have noticed, Holm, 28, and Maynard, 26, have stayed together -- putting a major show of PDA and togetherness -- despite that betrayal.

"Jef said their relationship isn't what it seems," ex Shepherd says.

Get all of the details on the bizarre Bachelorette cover-up -- and exactly how the pair struck a deal -- in the new Us Weekly, on stands Friday!