British Prince William\'s sister-in-law, Pippa Middleton, has been dumped by her literary agent after her party-planning book, \"Celebrate,\" didn\'t sell well. \"I am very sorry it has happened, but yes, it is true: I no longer represent Pippa and I wish her every good luck,\" the Daily Telegraph quoted Middleton\'s agent, David Godwin, as saying. Middleton is the sister of Kate, the Duchess of Cambridge and Prince William\'s wife of nearly two years. Starting next month, Middleton will write a column called \"Pippa\'s Friday Night Feasts\" for Waitrose Kitchen magazine, the Telegraph said.