Boro have brought the former Manchester City striker to the Riverside on a season-long loan from Valencia.
Boro have already brought in ex-Barcelona and Spain goalkeeper Victor Valdes, Ajax star Viktor Fischer, Valencia defender Antonio Barragan, and last season's loanee Gaston Ramirez amongst their signings so far in the transfer window.
Now, they have added Barragan's teammate Negredo for the season in a bid to boost a strikeforce which already boasts Jordan Rhodes, Cristhian Stuani, and David Nugent.
The 30-year-old is best remembered by English supporters for his solitary season with Manchester City in 2013-14, when he scored 23 goals in all competitions largely in the first half of the campaign.
However, injury cut short that lethal form and he failed to score for the Premier League side after the third week of January.
He has struggled to recapture his previous form in two years at Valencia since that season, netting just 10 times for the La Liga side.
Regardless of his recent struggles, however, Negredo represents another hugely ambitious coup for Aitor Karanka's promoted Boro, and fans of other clubs on Twitter could scarcely hide their disbelief after the deal was announced.
Middlesbrough actually got Negredo. That's mad.— Simo (@S1Moo_96) July 20, 2016
Negredo to Boro could be the best signing of the summer— Jack Schofield (@J_Schofield95) July 20, 2016
Alvara Negredo to Boro? What is happening in this transfer window?— Daniel Shaw (@shawzaam) July 20, 2016
Middlesbrough sign Negredo. Damn, they're showing ambition. Won't be surprised if the stay up this season.— Abhishek (@Memphisesque) July 20, 2016
Alvaro Negredo.. From Man City & Valencia to Middlesbrough.. Cracking signing from Boro, shows huge ambitions.— Joe Atkin (@JoeAFC_) July 20, 2016
Negredo is a cracking signing for Boro mind— LΛɄƦƎͶ ΔЧЯƎ (@LaurenSAFC92) July 20, 2016
Negredo to Boro is a belting deal.— Perry Smith (@PerrySmith45) July 20, 2016
So, Boro have confirmed Negredo on loan. Mad— Callum (@Callum_Massie) July 20, 2016
I can't believe Negredo has joined Middlesbrough lol— T.T (@FourFourPoo) July 20, 2016
As if negredo has gone Middlesbrough— Jake Byron (@jakebyron97_) July 20, 2016
Boro sign Alvaro Negredo. Imagine saying that 3 years ago— Cameron Eyles (@cameroneyles) July 20, 2016