SARAH PALIN "will absolutely go berserk" when she learns BRISTOL, 19,  is back with baby daddy LEVI JOHNSTON, says an Palin family insider

The ENQUIRER has learned exclusively that, unknown to Sarah, Levi has been secretly spending nights with Bristol at her townhouse in Anchorage.

Teen Prego Queen Bristol, who announced she was preggers during her mom’s 2008 GOP VP bid , is currently a celeb teen ambassador for  Candies, a group that promotes teen sex abstinence.

But that hasn’t stopped the rebellious teen from spending nights with the father  of their 18-month old son, Tripp, at her new, three-story townhouse about 30 miles from Wasilla.

"Sarah’s going to explode when she finds out Bristol has been sneaking Levi into her townhouse to stay the night."

FOR THE FULL STORY and all the detail of Levi & Bristol’s loving reunion – pick up the new ENQUIRER – now on sale!