The striker arrives from Palermo for a club-record fee to become the Tigers' eighth summer signing and will fill the void left be Shane Long following his move to Southampton.
The striker has penned a three-year deal, with the Tigers retaining the option of a fourth, to become the club's eighth summer signing on deadline day in a 9.5 million pound deal.
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On Wednesday, Steve Bruce turned his attention to the Uruguay international as Shane Long's replacement after Blackburn rebuffed the Premier League side's offers for Jordan Rhodes.
"Abel is a fantastic signing and highlights just how far the Club has come in such a short space of time," manager Bruce told the club's official website.
"He is an exciting talent and like myself, I’m sure the supporters can’t wait to see him in action."
Hernandez's arrivals marks the second time the club has broken its transfer record this summer following the £8 million deal to make former loanee Jake Livermore's move from Tottenham permanent.