The Mystery of Stieg Larsson

This weekend on "CBS News Sunday Morning," the family of author Stieg Larsson reveals to correspondent Erin Moriarty that the much-talked-about fourth book in his Millennium series is, in fact, really the fifth book.

Larsson is the Swedish novelist behind the best-selling books "The Girl With the Dragon Tattoo," "The Girl Who Played With Fire" and "The Girl Who Kicked the Hornet's Nest," which have become a worldwide literary phenomenon. The books portray what Larsson saw as the dark sides of Sweden, and the conspiracy theories surrounding Larsson's sudden death in 2004 have only further fueled their popularity.

Larsson had initially envisioned the Millennium series to consist of 10 novels, but died just before the first of three was published. Rumors of an unfinished manuscript swirled and Larsson's father says that it does exist and that he has seen and held it.

"I got the email from Stieg 10 days before he died where he wrote book number four is nearly finished," says his brother Joakim in his first U.S. television interview. "And to make it more complicated, this book number four, [is] book number five, because he thought that [it] was more fun to write than book number four."

And in the six years since Larsson's death, questions and controversies surrounding his legacy are at the center of a battle between his brother and father, who inherited the rights to the books and the millions they generate, and Larsson's girlfriend of 32 years, Eva Gabrielsson.

"We find out that we inherited everything and Eva just stopped talking to us," says Larsson's father, Erland.

"We want to work with Eva. She says 'no,'" adds Joakim. "We tried for nearly six years to get an agreement with her of some sort in any way. But she turned us down all the time for some reason."

Eva Gabrielsson declined CBS' request for an interview.