The American Horror Story star, 24, is said to have called off her engagement to co-star Evan just six months after accepting his proposal.
Multiple reports from the States claim they just grew apart.
People magazine states that "they both had a lot of growing to do and it was better that they do it on their own".
A source told Just Jared that "their three years together just ran its course, although the break-up was amicable".
Emma - who is Julia Roberts' niece - met Evan while filming Adult World and they went on to star in American Horror Story together.
They began dating in the summer of 2012, and confirmed their engagement in January 2014.
Evan has previously described Emma as his "best friend", while she called him "the coolest guy I know".
However, their three-year relationship was reportedly turbulent...
In the summer of 2013, Emma was arrested in Montreal following a domestic dispute that allegedly left Evan with a bloody nose. No charges were filed, and the couple later explained that it was simply a "misunderstanding".
While neither party have confirmed the split, they have not been pictured together for some time and she is no longer wearing her engagement ring.
Emma recently posted a message on Instagram which could be interpreted as a nod towards the split.
The statement read: "New month, new beginning, new start, new mindset, new focus, new intentions, new results."
She next stars in Ryan Murphy's new Fox series, Scream Queens, premiering in September 2015.
Meanwhile, Evan is currently shooting X-Men: Apocalypse where he portrays Quicksilver.
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