It's a done deal. Pippa Middleton has signed on the dotted line to write a party planning book. The winning publisher is Michael Joseph, an imprint of Penguin, who is believed to be paying the royal sister an advance of nearly $600,000, according to the Mail on Sunday.

The auction of Pippa's book had been rumored for weeks, and at one time it looked like HarperCollins was getting the tome.

‘It will be about entertaining and how to throw the perfect party. It’s not just about being the perfect hostess – it will also include recipes and information about how to host different types of events," a source told The Mail.

Pippa, 28, will not be employing a ghostwriter. This Martha Stewart-in-waiting already works as a writer and editor in the party planning field.

As RadarOnline.com reported just last week, Pippa's column, Party Time, for her parents' online party supply store, is a must read for anyone scheduling a festive gathering.

The schedule is to have the book out in time for everyone's 2012 holiday party planning.

Is Pippa Middleton going to be a Duchess too?

PHOTOS: Pippa And George Get Cozy

Rumors have been swirling that Kate Middleton’s younger sister is newly single, but she’s been spotted recently with her ex-boyfriend and maybe current flame George Percy, whose father is the Duke of Northumberland and one of the wealthiest men in England.

PHOTOS: Kate & Pippa Attend a Jockey Wedding

RadarOnline.com has a gallery of “Her Royal Hotness” Pippa with George at all the hot spots the pair have hit up lately.

Pippa and George met and dated when they were students at the University of Edinburgh, and they were even roommates for a while.

An online party planning business owned by Kate Middleton's family has just signed a lucrative deal with Justin Bieber to market some of his merchandise.

Party Pieces now has the rights to sell several Bieber items including the Justin Bieber Party Kit - a $35 set which includes plates, cups, napkins and balloons for16 people.

PHOTOS: Prince William & Kate Walk Hand-In-Hand

It even includes a huge banner sporting an image of Justin himself.