What happened to the former P.E. teacher who beat Manny Pacquiao?
The Australian delivered one of the biggest upsets in modern times by outpointing a boxing great in Brisbane.
Especially when you consider the Filipino icon posted a Twitter poll asking fans who they wanted to see him fight; Amir Khan was top with 48 per cent while British foe Kell Brook was in second place with 24 per cent - Horn meanwhile got just 7 per cent.
When a showdown with Khan collapsed in the UAE, Pacquiao turned to the Australian. He was a relatively unknown name unless you lived in Australia or New Zealand.
Before facing Pacquiao - boxing's only eight-division ruler - Horn was undefeated in 17 bouts and ranked No.2 with the WBO.
Promoter Bob Arum said it was a treat for Pacquiao fans and promised it would be an entertaining fight for those tuning in.
In what was, in all honesty, a scrappy and rather dull, poor encounter, and one which nearly got stopped in round nine after an onslaught from Pacquiao, the world would go on to witness one of the most shocking results of the decade as Horn got his hand raised by Mark Nelson.
Pacquiao intended to trigger his rematch clause but later pulled out due to his commitments as a senator in the Philippines.
It saw Horn make a successful first defence of his WBO crown with a stoppage win over Britain's Gary Corcoran but the Queensland star would relinquish the belt to Terance Crawford in his sole fight in America at the MGM Grand.
Since then, he has racked up two wins and avenged his defeat to Michael Zerafa at middleweight. Horn's most recent bout was against Tim Tszyu - the son of former light welterweight king Kostya Tszyu - who British fans remember more for his devastating defeat to Mancunian Ricky Hatton in 2005.