Vertical alignment with cases environment

I hope this question is not duplicate: How is it possible to align all of these equals signs? The main problem is the cases environment, because I don't know how to reference the &-Operator.

Thank you very much in advance!

\documentclass{scrartcl}\usepackage{amsmath}\usepackage{mathtools}\begin{document}\begin{align*}a+b&=0\intertext{some text a}c+d&=0\intertext{some text b}\begin{rcases}\lambda_a &= x\\\lambda_b &= y\end{rcases} \quad \text{some text c}\end{align*}\end{document}