Jessica Simpson says the success of her memoir is ''humbling and surreal''.

The 39-year-old star has seen her new memoir, 'Open Book', top the New York Times best seller chart, and Jessica now has taken to Instagram to show her appreciation to the people who've supported the book's launch.

She explained: ''I wrote this book thinking if it could help one person get through their struggle it would be worth it. To find out that I have sold enough copies to make me the #1 New York Times best seller is humbling and surreal.

''I pray every day that I can use my platform for good. I promise to continue to be open and to lead with my mistakes. I promise to be honest and use the voice that God gave me.

''Thank you guys for standing by me and supporting me. This is a dream come true. #OpenBook (sic)''

In the memoir, Jessica speaks candidly about various aspects of her personal life, including her high-profile marriage to Nick Lachey between 2002 and 2006.

And the blonde beauty recently admitted she regrets not getting a pre-nuptial agreement when they tied the knot, as she was convinced they would be together forever.

Jessica - who is now married to retired sports star Eric Johnson - said: ''I wish I would have signed a pre-nup. That's the funny thing: Nick wanted me to sign a pre-nup and I was so offended.

''I'm like, 'But we're going to be together for the rest of our lives. We're saying our vows to God and in front of all of our family and friends. This is never gonna end.′ And we didn't sign a pre-nup.''