former teacher mary kay letourneau and her student-turned husband , vili fualaau , have revealed how their relationship became sexual when he was just 12 years old .
on the eve of their 10th wedding anniversary , letourneau , 53 , and vili fualaau , 31 , sat down for an interview with barbara walters for ' 20/20 ' , which will air tonight .
the couple , who have two teenage daughters , met when fualaau was in her second grade class in seattle .
` the incident was a late night that it did n't stop with a kiss , ' letourneau recounted .