The notorious Colombian kingpin's bro, Roberto, is suing Apple for a whopping $2.6 BILLION, claiming someone hacked his smartphone and found his address through FaceTime, even though he claims an Apple employee assured him the iPhone X was the most secure on the market.

According to the lawsuit, obtained by TMZ, Pablo's brother bought an iPhone X back in April 2018, and he claims the security promise fell horribly flat. One year after buying the X, Roberto claims he got a life-threatening letter from someone named Diego, who said he found Roberto's address through FaceTime.

In the docs, Pablo's bro says he had to relocate for his safety, and lost a ton of money beefing up his security ... not to mention the emotional distress he says he suffered as a result of the security breach. Roberto claims he had several assassination attempts on his life before buying the iPhone X, and only bought the phone because he'd been assured his info would be safe from hackers.

In the suit, Roberto says he conducted his own investigation after receiving the letter, and found his iPhone had been compromised due to a FaceTime vulnerability.

Pablo's brother is not stopping at a lawsuit ... Roberto is also going after Apple's bread and butter.

Roberto just launched a limited edition gold-plated iPhone 11 Pro 256GB, which his Escobar Inc company is hawking for $499. Roberto says it's his way of fighting Apple -- selling their phones at a lower price, with gold-plating and sexy girls showing off the phones.

Pablo's brother says ... "Apple can never do that."

Roberto also bought and launched the domain name www.ripapple.com, which links to his gold-plated iPhone. He says the website will have "proof showing how the people of the world were scammed by Apple Inc, buying crap for crazy prices."

If he wins the lawsuit, Roberto says he will share the dough with people who bought iPhones and "ultimately donate it all."

We reached out to Apple ... so far, no word back.