Newcastle United have announced the permanent signing of Mikel Merino after a fine start to life at St James' Park.
But Merino has quickly won a place in the Newcastle side - starting six of their seven Premier League games - and they have now activated a clause to seal his signing on a five-year deal.
"I'm really happy to be here and for this part of the contract to finally be official," Merino told the club's official website.
"I'm happy to be here for five more years and I hope to keep playing for this club and to give good things to all the people and the club."
Manager Benitez added: "I'm really pleased we have been able to bring Mikel to the club permanently. He has played very well since he joined us.
"He has settled in quickly, has a lot of quality on the ball and is keen to learn – that is a crucial part of his future development."