Captain Underpants and the Terrifying Return of Tippy Tinkletrousers is a 2012 American children's novel and the ninth book in the Captain Underpants series by Dav Pilkey. It was published on August 28, 2012, six years after the publication of the previous book. Tippy Tinkletrousers is actually Professor Poopypants, as revealed in the previous book. This book explains how Tippy Tinkletrousers arrived at the end of the eighth book, as well as a prequel story of George and Harold in kindergarten explaining how their friendship began and setting the page for their life before Captain Underpants.