The video, which was first published by TMZ, showed Solange Knowles lashing out in a lift after the Met Gala on May 5.
A security guard intervened in the apparent altercation. There is no audio on the recording.
The Standard Hotel said it was “shocked and disappointed” by the leak and had identified the person responsible.
The employee was fired for “breaching the security polices of the hotel and recording the confidential CCTV video”.
The Standard Hotel added it would turn over “all available information to criminal authorities”.
Representatives for Jay Z, Beyonce and Solange Knowles have made no comment on the video.
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