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Sure, Chief Webber (James Pickens Jr.) and Mer's mom, the brilliant surgeon Ellis Grey (played by recurring guest star Kate Burton), were married to other people when they began their love affair back in the day. But it was torrid enough to tear Mer's home life apart and deliver us a surprise love child in the form of Maggie Pierce (Kelly McCreary), whom we first met in season 10 and has since become a cornerstone of the series. It was an illicit love that would never last, not least because Ellis was ravaged by Alzheimer's until her death in season three. But it had so much impact on just about everything.