Gucci Mane's Brother Terribly Sad He and Mom Weren't Invited to Wedding

Gucci Mane gave his mother and brother a fierce cold shoulder because they were not invited to his lavish wedding ... so says Gucci's youngest brother.

Nate tells us he has no idea why the rapper left him and their mom, Vicky, off the guest list for $1 million affair at Miami's Four Seasons Hotel.

Nate, who's gotten shout-outs from Guwop on tracks like "Rude," says he's happy for his big brother but sad no fancy invitation was sent his way. Adding insult to injury -- another brother, Duke, was Gucci's best man.

Little bro says the diss sends a clear message, and Keyshia Ka'oir should pay attention.