Paul Smith believes Saul Alvarez has overlooked his brother Liam - and will pay the price on Saturday night.
'Beefy', the WBO super-welterweight world champion, takes on the Mexican star in Texas, with his older brother predicting a major surprise.
Paul Smith admits his 28-year-old sibling is the huge underdog, but is convinced he has the power to become only the second fighter, after Floyd Mayweather, to beat 'Canelo'.
"Liam is one of the most spiteful guys I've been in the ring sparring with," he said.
"He's a spiteful type of fighter. He's quality, a thinking man's fighter and he'll break you down mentally and physically as well.
"He's got amazing variety which is second to none, and I just think 'Canelo' will overlook him - and has overlooked him.
"People are all overlooking him. 'Canelo' is looking at fights - I've seen plenty of names - for November/December, and Liam's happy with that. We want 'Canelo' to overlook him.
"I think Liam is a very underrated fighter because he hasn't been showcased as much as he should have been in his career, but it's probably going to work in his favour on Saturday."
Paul Smith, who flew out to America on Monday, is also a 'Canelo' fan and admits he is expecting a classic at the AT&T Stadium in Texas.
He, as well as former Rotunda gym-mate Tony Bellew, believes Liam Smith has more power than people give him credit for and he will show that when he takes on the biggest test of his career.
"Canelo is quality, very good at what he does and it's a similar style to Liam's - the styles are going to gel," said Smith.
"That's the key to this fight; whatever way it goes, it's going to be a classic and it's going to be a very good fight.
"Liam is a big underdog, especially to everyone who isn't around him like Joe Public and the Americans, who don't know him.
"But he is a world champion, he's a quality fighter and he hasn't been beaten and he's been looking absolutely brilliant in the gym. He's looking great and I know he can punch. If you've been in the gym with him, you'll know what I mean.
"The hard work has been done now for Liam and he's going to pull off massive surprise and beat Canelo. And the future is massively bright for him."