Prince Harry -- Offered $10 MILLION to Bone on Film

You knew it was coming ... and now, so does Prince Harry -- a multi-million dollar offer to get down and dirty in a XXX movie ... courtesy of the biggest porn studio on the planet.

Vivid Entertainment honcho Steve Hirsch just fired off a letter to the royal palace in London -- offering Prince Harry $10 million to star in a big budget adult film called "The Trouble with Harry" ... thanks to his recent naked romp in Vegas.

According to the letter, the film would also star "little Harry" and would feature some REAL royal carousing -- in the form of full-on boning.

Hirsch writes, "We assure you the sex will be well-scripted, and the crown jewels will not be 'minimized' in any way."