According to US Weekly, the singer and the Oscar winner plan to tie the knot in March, apparently in Australia, where the two superstars grew up. Previous marriage rumors have generally been vague, but in this instance, the magazine asserts that invitations to the big event have already been sent. Neither Keith nor Nicole has ever confirmed an engagement, though the two showed up together at the recent Grammy awards show and are frequently spotted around Nashville at various locales. Keith's label has no knowledge as to any official word on this latest report. But we'll keep you posted.