The heartbreaking reason behind Donald Trump's sobriety

During a press conference earlier this morning, Donald Trump made a joke about how he doesn't drink alcohol.

Trump was questioned about his testimony in an FBI investigation in which he mentioned his drinking habits. 

"I'm not a drinker. I can honestly say I never had a beer in my life. It's one of my only good traits," he responded.

"I never had a glass of alcohol. I never had alcohol, for whatever reason," he added.

"Can you imagine if I had? What a mess I would be. I would be the world's worst. I never drank, OK?"

READ MORE: 

• Donald Trump attacks Meryl Streep over her speech at the Golden Globes 

Despite the light-hearted response and the laughter that came after, the backstory behind Trump's sobriety isn't exactly light-hearted. 

Just last year during an emotional speech declaring the US opioid crisis, Trump opened up about how his brother died far too young. 

"I had a brother, Fred," he said.

"Great guy, best-looking guy. Best personality, much better than mine.

"But he had a problem, a problem with alcohol. And he would tell me, don't drink.

"He was substantially older and I listened to him and I respected. He's also added, don't smoke.

"But he would say it over and over again. And to this day I've never had a drink. And, I have no longing for it. I have no interest in it.

READ MORE: 

• Donald Trump announces his running mate - little Donald! 

"To this day I've never had a cigarette. Don't worry those are only two of my good things — I don't want to tell you about the bad things. There's plenty of bad things too."

When wrapping up the speech, Trump mentioned how he hoped that Fred's death would serve as a lesson to young people. 

"But I learned because of Fred and that's what I think is so important. This was an idea I had — if we can teach young people not to take drugs, not to start, then it's really easy not to take them. I think that's going to be our most important thing."