Mitt Romney -- Author Who Saw Divorce Transcripts Says Romney Didn't Tell Truth About Staples

The ex-wife of one of Mitt Romney's closest advisers says Mitt lied on the witness stand in her divorce about a key asset -- the value of Staples, the company her husband founded -- and as a result she was grossly shortchanged in the property settlement ... this according to an author who helped the ex-wife write her story.

Sadi Ranson says she reviewed the transcripts of the divorce between Staples founder Tom Stemberg and his wife Maureen during the collaboration on the book. Ranson tells TMZ ... she reviewed boxes and boxes of transcripts and claims Romney testified the Staples stock was a pipe dream because the company was not successful -- something Maureen says was flat-out untrue.

The Boston Globe goes to court today in an attempt to unseal the transcripts and lift the gag order on the case.