In its 43-page lawsuit, which was filed in federal court in Delaware, X Corporation alleges trademark infringement, adding that despite Bluebird’s “purported plan, it cannot bring Twitter ‘back’—Twitter never left and continues to be exclusively owned by X Corp.”

The startup claims X Corp. ‘legally abandoned its rights’ to Twitter’s brand.

In response to a recent trademark petition claiming X had abandoned the Twitter name, the company updated its Terms of Service today.

A Virginia startup calling itself “Operation Bluebird” announced this week that it has filed a formal petition with the US Patent and Trademark Office, asking the federal agency to cancel X Corporation’s trademarks of the words “Twitter” and “tweet” since X has allegedly abandoned them.