Turunen was axed in a letter from her former colleagues, who accused her of "greed, underestimating the fans, and breaking promises".
But she has told two press conferences she had decided to leave Nightwish in December 2004, and was making one final album with the band.
She says, "There were big problems. The next album would have been the last one."
Turunen now intends to concentrate fully on her already successful solo career.