In honor of being the first NFL team to reach one million Twitter followers, the New England Patriots created customized jerseys as a thank-you for a few fans who retweeted them, featuring each follower’s Twitter handle on the back.

During this promotional activity on Thursday, Nov. 13, the team’s filtering system made a dire mistake, and created a jersey for a Twitter user whose handle included a highly offensive racial slur. It was not long before the controversial mistake went viral- the offensive tweet received 586 retweets and 299 favorites before being taken down.

The Patriots tweeted on Thursday night in an attempt to mend their error.

“We apologize for the regrettable tweet that went out from our account. Our filtering system failed & we will be more vigilant in the future,” they said.

The tweet remained on the Patriots’ Twitter page for a whole hour, shocking and upsetting viewers, before the mistake was realized and the tweet removed.