Rumours earlier this year suggested the two were on the verge of a split over Cowell's reluctance to commit.
Now 34-year-old Seymour has apparently told pals that the couple have gone their separate ways.
"We've split up. It's very sad but we decided to go our separate ways. It just wasn't working out between us," she said to friends, according The Mirror.
"There's no one else involved and we want to remain friends."