Bristol Palin said today that Sarah Palin definitely knows whether she will run for president next year -- but she's not sharing what those plans are.

She definitely knows. We've talked about it before. But some things just need to stay in the family, the younger Palin said in an appearance on FOX & Friends, where she was plugging her book, Not Afraid of Life: My Journey So Far.

In her memoir, the 20-year-old takes shots at the family of Arizona Senator John McCain -- whose choice to make Sarah Palin his 2008 running mate catapulted her to political stardom -- and reveals how she drunkenly lost her virginity to Levi Johnston.

She also writes about being in the media spotlight when she was pregnant during the 2008 campaign, saying, For some reason, I didn't realize the ripples my pregnancy would cause throughout the nation.

Not Afraid of Life, written with Nancy French, was published last week by HarperCollins (272 pages, $25.99).

After a bevy of television and radio appearances today, Bristol Palin will have her first book signing tomorrow at the Mall of America in Bloomington, Minnesota -- with her mom, who will be signing her latest book, America By Heart.

Sarah Palin has called her daughter's book shocking, refreshing, honest, inspiring, and perfect. In a new statement, Sarah Palin said she is so proud of Bristol Palin and thrilled to be joining her to kick off her book tour, according to the Associated Press.

Bristol Palin will then promote Not Afraid of Life at a Books-A-Million in Birmingham, Alabama next Tuesday, followed by what is sure to be a gabfest on The View on Thursday, July 7, according to HarperCollins.

(With material from Reuters)