Sebastian and Gabriela Fundora are likely the toughest siblings in all sports

• Sebastian and Gabriela Fundora compete in separate matches Saturday in Carson.
• The brother-sister combo may well be the toughest siblings in all sports.

Sebastian and Gabriela Fundora epitomize the saying "don't judge a book by its cover" more than perhaps any other fighters in boxing.

They may look like they'd help your grandma across the street with her shopping, or ace any algebra test you can throw at them, but, make no mistake, the Fundoras can kick all your asses.

Insider has reported on Sebastian Fundora's fighting throughout the year and has become familiar with him inside and outside the ring.

At the International Boxing Hall of Fame weekend in June, we saw him in the Canastota museum where he hung out like a regular combat sports fan. He would have blended seamlessly into the crowd if it weren't for his gangly, 6-foot-6 frame.

The way he looks, and talks, is a sharp contrast to who he is inside the ring as we witnessed his savagery earlier this year in April, when he bludgeoned Erickson Lubin in what remains, for us, the Fight of the Year.

Sebastian returns Saturday for a super welterweight fight against Carlos Ocampo at the Dignity Health Sports Park in Carson for a Premier Boxing Champions event broadcast on Showtime.

But he's not the only Fundora fighting that night as, earlier in the evening, Gabriela steps through the ropes for a bout of her own.

Judging by the way Sebastian talks, it's Gabriela we should be worried about as he claims she's the better fighter.

The Fundoras may well be the toughest siblings in all sports

The way Fundora performed against Lubin showed, on a big stage in Las Vegas, that he had the heart required to overcome challenging moments against a proven puncher, and the ability and skillset to stamp his authority against a top-tier opponent.

The 24-year-old has long been touted as one of boxing's best prospects in previous years but after the Lubin knockout, in which he boxed viciously from close range rather than rely on his height and reach to pick him off with shots from distance, Fundora showed that he's the division's scariest contender to the undisputed champion Jermell Charlo.

But he has hinted through the months to Insider that he may not even be the toughest fighter in his own family — that could be Gabriela.

"I'm very excited she's fighting on my card as she's got such a big future in women's boxing," Sebastian told Insider ahead of his Saturday fight, and Gabriela's match against Naomi Arellano Reyes.

"With women's boxing on the rise it's great that Showtime is putting on these events because these girls deserve the platform.

"There's never been a doubt in my mind that she'd become a world champion," he said.

When we told Gabriela about her brother's assessment, she said: "You know what? Sebastian is a very wise man — he got that right."

A sibling rivalry drives the Fundoras forward

Ever since they were kids, Sebastian and his Gabriela, 20, were always trying to one-up each other.

"He keeps me on my toes, that's for sure," said Gabriela.

Even when they were at school, one of the Fundoras would come home with their report card knowing they had straight-A grades, and look at their siblings to check if they'd dropped to a B.

Whoever had the best grades would have "bragging rights" for the rest of the year.

Their competitiveness extended into video games like Mario Kart, chess, and even the running track where they'd try to outdo each other's personal best times.

According to Sebastian, he's the better chess player. He says he's cerebral, trying to implement strategy. Gabriela, she said, has seen 'The Queen's Gambit' and derives her expertise from that.

If you speak to Gabriela, she'll be happy to tell you about their karaoke battles — something Sebastian, perhaps conveniently, failed to.

She sings ABBA, David Bowie, and Elton John. "I love the classics," she said, before calling Sebastian "a little shy" on the microphone, before he eventually belts out Guns N' Roses, ACDC, and Metallica.

"I am much better," she said.

They are both determined to deliver fireworks with their knockout power this weekend

Women's boxing is on the rise, with athletes like Katie Taylor, Amanda Serrano, and Claressa Shields generating mainstream attention on both sides of the Atlantic.

Gabriela is one of the new generations and hopes to lead "a whole new level of boxing that's evolving a lot and becoming bigger."

Gabriela's goal ahead of her flyweight fight is to win, in style, and then return backstage to help Sebastian prepare for his bout against Ocampo.

She said: "I want fireworks and put on a good show for the public."

Sebastian, too, is used to delivering fireworks considering his explosive win over Lubin, and wants to do the same to Ocampo before they celebrate as a family by watching their beloved LA Rams team take on the Cowboys on Sunday.

Weeks later, they'll be taking their mom and family on a cruise, leaving from Long Beach and vacationing along the Mexican beaches.

The way they both talk, they want to share their successes together because, despite their rivalry, they have the same dream — to become world boxing champions at the same time.

"That dream is becoming a reality," Sebastian told us. "And it's so great to experience that with my sister. Who else do you want to be there with you than your sibling?

"I want my sister there, always."