Alexander arrived at USYK London and sent a message to Anthony Joshua before his heavyweight performance.
The former undisputed cruiserweight King will challenge AJ for the unified heavyweight title in front of a sold-out crowd at Tottenham Hotspur Stadium on Saturday night.
Usyk, 34, is preparing for his first crack at heavyweight gold in his homeland Ukraine, which he left on a private plane Monday morning.
Kat shared pictures of herself and her team about boarding a private jet on Instagram early Monday.
His entire crew donned fluorescent turquoise tracksuits for the trip.
The caption accompanying the post read: “#SpaceX #Jaxet #UsykJoshua.”
The Ukrainian entered the UK and gave AJ a message, simply saying: “Hello Anthony, here I am.”
Usyak’s clash with Joshua, 31, will be his third outing in the heavyweight division – which he gatecrashed in October 2019.
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But the Olympic gold medalist worries more about her son’s first days at school than his bid to become a two-division world champion.
The Cat said: “At the moment I don’t think about Anthony Joshua.
“I don’t think about what he will do, what he will use or how he will box.
“I just have a little time to finish my training camp, all I can think about.
“Right now I think more about how my son feels at school because he just started first grade and he really didn’t want to go and do that.
“He was saying: ‘I don’t want to go to school, Dad. I’m bored at school and you’re not there.’
“But now everything is fine, he seems to have calmed down.
“So I probably think more about what Anthony Joshua would do in the ring.”
Right now I think more about how my son feels at school because he just started first grade and he really didn’t want to go and do it.
Oleksandr Usik on his struggle with Anthony Joshua
Usyk scored a unanimous decision victory over Derek Chisora in his last outing last November, but was less than impressed with his performance.
And the cunning southpaw believes Joshua’s team will be in for a rude awakening if they expect an easy victory on the back of their last outing.
He said: “I am very grateful to everyone who supports me and everyone else but they expect too much from athletes.
“Some of them very much don’t understand what is happening in the ring, how difficult it is or in some cases how easy it is.
I Joshua vs Usyk: All the TV, streams and undercard info ahead of Saturday’s heavyweight match
“People just have an image of what they think of.
“The fact is I boxed Derek for 12 rounds but he’s actually a really tough guy to beat.
“If you look at his two fights with Tyson Fury, he’s gone 22 rounds with him.”
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