# Latest MiKTeX-Update broke XeLaTeX with fontspec

I updated MiKTeX a few days ago and since then I cannot compile XeLaTeX with fontspec anymore.

\documentclass{article}
\usepackage{fontspec}

\begin{document}
Hello world!
\end{document}

When I try to compile it MiKTeX tells me that it expl3 is an unknown package. I cannot find this package in the Package Manager. Without the \usepackage{fontspec} the file compiles fine.

Any idea what I can do?

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