How do I explain why I left my last job?

My last job was a 6 month contract, however the contract could be extended. I did well at the job and passed my 6 month probation period. A week later I finally spoke up about a co worker that I was sitting next to. She has been at the job 7 years and is very competent, but a nasty person. She was gossiping about... show more My last job was a 6 month contract, however the contract could be extended. I did well at the job and passed my 6 month probation period. A week later I finally spoke up about a co worker that I was sitting next to. She has been at the job 7 years and is very competent, but a nasty person. She was gossiping about me and other colleagues, making rude and threatening comments and named and shamed many people including myself. A week later they allowed me to move my desk so I wouldn’t be sitting next to her, and on the same day they told me they had found someone better suited for the job and had to let me go. Coincidentally, 2 of their other employees were also fired shortly after complaining about this woman. So I have a job interview tomorrow and when they ask me why I left my last job, what do I say? Would it make me look bad for telling the truth?
Update: I told the hiring manager that it was a 6 month contract but she asked if there was a chance it could have been extended. Just incase I am not successful in the interview tomorrow, what should I tell the next person that asks me this? Do I say it was only 6 months with no extension?
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