Get ready for what may be the messiest love triangle ever on Grey's Anatomy.

The Season 13 premiere picks up just minutes after the Season 12 finale, when Maggie (Kelly McCreary) confessed to her sister Meredith (Ellen Pompeo) that she's got the hots for Nathan Riggs (Martin Henderson). The problem? Meredith and Riggs are already getting it on.

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Meredith opts to keep her mouth shut for now, so we'll have to wait until at least Episode 2 to find out what Maggie's reaction is to the news - but you can bet it's not going to be pretty.

"One of the things that we know about Maggie is that she is really a stickler for honesty and the truth," McCreary tells TVGuide.com. "In her first season, she really holds it against Richard that he didn't tell her [he was her father] right away, that he withheld the truth for any length of time. ... To me, that's an indication of how we can expect Maggie to feel about any lack of honesty, any lack of full transparency and disclosure in a relationship - especially with somebody that she trusts and, more than trusts, really relies upon as much as Meredith."

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