Levi Johnston shopping tell-all to finance custody battle for son!

Gov. Sarah Palin's worst nightmare is coming true! Her grandson's dad is shopping an explosive tell-all book targeting the former vice-presidential candidate, say sources.

It's the latest shot fired in the all-out war between the families of the Alaska governor and 19-year-old Levi Johnston, the estranged father of Sarah's grandson Tripp.

"Levi was right there in the middle," a source told The ENQUIRER. "He knows what really happened inside the Palin family."

Levi says he has been  banned by the Palins from going on outings with his baby son, and he believes a tell-all book could help pay the legal bills in an anticipated custody dispute, say sources close to him.

A pal of Levi's told The ENQUIRER that the young father is eager to write the book to provide financial security for his son Tripp and himself, to set the record straight.

"If Levi could get a million bucks, it would be worth telling all he really knows." said the source.

What are the secrets Levi's kept undercover for months about ex-Bristol and Palin son Track?!

 Pick up the latest ENQUIRER for all the details!