Levi Johnston, Sarah Palin

Levi Johnston says fame has gone to Sarah Palin's head.

"Being up there and running for vice president — it's totally different than governor. There are cameras every day, she had Secret Service, you name it. And just seeing how she acted after it was all gone, I just think that it definitely got to her head," Levi Johnston said during a Today show interview on Monday.

Check out pictures of Palin on Saturday Night Live

The 19-year-old father of Bristol Palin's 7-month-old son, Tripp, said that while Palin is "an incredible lady," she was not always "up-front with everybody" — in this case, about the reason for her resignation.

Watch Palin explain her decision in a recent interview

Johnston said money played an important role in her decision to step down as governor of Alaska. "That's definitely part of it that she hadn't mentioned."

Johnston, who lived with the Palins for part of last winter before his engagement to Bristol was called off, also said Palin's HarperCollins book deal is worth between $7 million to $9 million. He did not say where he learned of the number.

Watch the full interview below: