My Author Page goes to the second slide of my Beamer presentation

I am using the following code to create a basic Beamer presentation where the first slide is the author and the institute slide and then comes the table of contents slide and then the content of the presentation (by frame) but using the code following :

documentclass{beamer}
usetheme{Boadilla}

title{My Presentation}
subtitle{Using Beamer}
author{Joe Bloggs}
institute{University of ShareLaTeX}
date{today}

begin{document}
begin{frame}
frametitle{Outline}
tableofcontents
end{frame}
begin{frame}
titlepage
end{frame}


begin{frame}
frametitle{Title}
section{Section 1}
subsection{sub a}
end{frame}
end{document}

The author slide is placed at the second position after the table of contents slide. Why ?

Thanks for the clarification.