That's "Shark Tank" star Barbara Corcoran warning Patrick Mahomes that with giant fortune comes giant scammers trying to take your money!

But, if you know anything about Barbara, you know she's a gangster when it comes to finance ... and she's dishing out some sage advice for the QB so he can STAY RICH for the rest of his life.

So, what should the KC Chiefs QB do with the $500 mil he's expected to make over the next 12 years?

"First of all, it's not $500 million," Barbara says ... "Remember, he has an Uncle named Sam. He's gonna have to pay him $250 million so he really only has $250 million. Bear that in mind."

Corcoran explains, "The first thing he should do is put it in the bank. Not do a thing! I know because when I sold my business, every creep came out of the woodwork with a $10,000 problem. Everybody is after your money and you can't trust anybody."

Barbara says it took her at least a year to realize how to turn people down effectively -- and the key is to hire a "bad guy" to tell people "no."

"The most important thing is before he buys that big house and a big jet ... he's gotta figure out how much money he needs to live on."

"He's a kid but he's gonna live a lot of years! So for every $25 million he puts away, he's going to get a $1 million income for the rest of his life"

"He should figure out, I need $1 million? I need 2 million? I need 5 million? And put that money aside. That's what he's gotta do."

Corcoran says Patrick should spend some time with her "Shark Tank" pal Alex Rodriguez -- who has become a major real estate investor.

That's saying something considering A-Rod reportedly made more than $441 million in MLB contract money!

There's more ... Corcoran also has a business strategy for Patrick -- and it's pretty damn smart! Watch the video and if you have the money, you might wanna take her advice!!

She also offered this final warning to the 24-year-old NFL superstar ...

"Let me tell you something, the more money you make, the more creeps you attract. The more people dressed in fancy suits, and not some fancy suit, friends or family -- all come out and are after your money."