Unwanted Space when citing in theorem header

Question

Could someone please provide me a clue, why the following minimal working example produces the output

Theorem 1 ( [1]). Lorem ipsum.

instead of

Theorem 1 ([1]). Lorem ipsum.

(notice the unwanted space before the citation).

\documentclass[11pt]{article}

\usepackage{amsmath}
\usepackage{cite}
\usepackage{amsthm}

\newtheorem{theorem}{Theorem}
    \newtheorem{lemma}[theorem]{Lemma}



\begin{document}

\title{Title}
\maketitle

\begin{theorem}[\cite{articlexy}]
    Lorem ipsum.
\end{theorem}


\begin{lemma}[Text]
    Bla bla.
\end{lemma}


\bibliography{refArticlesAndBooks}

\end{document}

The bib-File is the following:

@article{articlexy,
 author = {Author Name},
 title = {Title of Paper},
 journal = {Journal},
 volume = {837},
 number = {6},
 year = {2003},
 pages = {255\nobreakdash--354},
 }

Thank you for your help.