Donald Trump has never had a sip of alcohol—and the reason is deeply personal. While many U.S. adults drink regularly, Trump remains teetotal due to a tragedy that hit close to home.

In a 2018 press conference, Trump revealed that his older brother, Fred Trump Jr., struggled with alcoholism and died at just 42. “He had a problem with alcohol… and he would tell me, ‘Don’t drink. Don’t drink,’” Trump shared. Deeply affected by Fred’s decline, Trump vowed to stay sober.

“I saw what alcohol did to him even physically… it had an impact on me,” Trump told The Washington Post. He believed drinking might’ve derailed his own life: “It’s very possible I wouldn’t be talking to you right now.”

Though he once promoted a vodka brand and his businesses serve alcohol, Trump personally avoids it. Aides say he swaps liquor for Diet Coke, a reflection of his competitive, disciplined nature.

Trump’s lifelong sobriety is less about image—and more about honoring a promise made to his brother.