Zac Efron sparked outrage on social media after posting a controversial tweet on Jan. 18, which is celebrated as Martin Luther King Day.

"I'm grateful for a couple things today: Martin Luther King Jr & 10 million followers on IG," the "Dirty Grandpa" actor tweeted on Monday, a post that drew criticism from his fans for using the holiday and his Instagram follower count in the same sentence, according to People.

"@ZacEfron This is one of the most offensive/diminishing/disrespectful things anyone has said in relation to MLK today. Get over yourself," one of Efron's several followers tweeted. Another user suggested Efron delete his account for posting the offensive tweet, which has since been deleted.

Less than 24 hours later, the actor took to Instagram to apologize for his post. "I have nothing but the greatest admiration and respect for Dr. Martin Luther King Jr. I realize that last night's post was completely insensitive and I apologize to anyone who I may have offended. So sorry," he wrote.

After "Dirty Grandpa," the 28-year-old actor will be seen in the comedy, "Neighbors 2" alongside Rose Byrne, Seth Rogen and Chloe Grace Moretz. The film's trailer dropped on Tuesday - Watch it HERE!

A photo posted by Zac Efron (@zacefron) on Jan 19, 2016 at 2:27pm PST