Starred chapter title with no chapter number in either toc or header

I am in the same situation as the author of How can I display a short chapter name in the header and a long chapter name in the TOC but, in addition, I also want the starred version for the Epilogue: no chapter number anywhere.

Here is a MWE:

    \documentclass[11pt]{book}\begin{document}\tableofcontents\chapter{Un El\'ephant}\c ca trompe,\chapter{Deux El\'ephants}\c ca trompent, \newpage\c ca trompent, \chapter{Trois El\'ephants}\c ca trompent ...\newpage ... \'enorm\'ement. \chapter*[SpryRogue]{Epilogue}\chaptermark{PiLog}             \newpagePas trop n'en faut. \end{document}