"Avi" could refer to several authors, including:
* Avi, the pen name of American author Edward Irving Wortis. His last book was "The True Confessions of Charlotte Doyle" which was published in 1990.
* Avi, the pen name of author Evelyn Waugh. He wrote numerous books before his death in 1966, and his last published work was "The Ordeal of Gilbert Pinfold" in 1957.
To determine the last book written by the Avi you're referring to, please provide more context, such as the author's full name or the genre of the books.