Actually I lied, it's the key of Cm. Same chords as Eb major. It also depends on the tonality. If the entire song is in a minor tonality it's Cm. If there is emphasis on the major aspect than it's Eb. But to be in key, the D should be diminished but maybe they substituted a D chord, I don't know. In fact, what the hell do I know, I'm no expert by any means.
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