Donald Trump is often speaking out against "fake news," but the United States President tweeted out a debunked rumor in response to Thursday's terror attack in Barcelona.

A van driver plowed into dozens of people on a busy tourist boulevard in Barcelona, killing 13 people and leaving 80 bloodied and battered on the pavement. Two people were arrested in the terrorist attack. ISIS' media wing, Amaq, issued a statement through social media calling the perpetrators of the assault "soldiers of the Islamic State," triggering the controversial tweets from Trump.

"Study what General Pershing of the United States did to terrorists when caught," Trump tweeted. "There was no more Radical Islamic Terror for 35 years!"

Trump was likely referring to a mythical practice of Gen. John J. "Black Jack" Pershing who supposedly killed Muslim rebels in the Philippines by shooting them with bullets dipped in pigs blood or burying them with the bodies of pigs, which Muslims are forbidden to consume. There were rumors that Pershing employed these tactics following the Philippine-American War in order to deter insurgents.

Several historians and myth-busting websites have debunked the claims. Additionally, Trump's claim that Pershing ended terrorism in the Philippines for 35 years is untrue as well and is easily proven by the violence that continued for decades after the rebellion that ended in 1913.