Levi Johnston Writing Tell-All Book

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Levi Johnston is ready to share his story with the world.

The 20-year-old Alaskan native -- famous for fathering a son with Sarah Palin's teenage daughter Bristol, now 20 -- is writing a tell-all book, a source confirms exclusively to Us Weekly.

Titled Deer in the Headlights: My Life in Sarah Palin's Crosshairs, the memoir is slated for a fall release under Touchstone Publishing.

"He's ready to give an inside glimpse to his relationship with the Palins, share his trials and tribulations of being thrust into the spotlight and becoming a father at such a young age," the source tells Us.

In the meantime, Johnston -- who broke off his second engagement to Bristol last July -- is planning to celebrate his 21st birthday at Chateau Nightclub & Gardens in Las Vegas on May 6.