It's been a whirlwind few hours for Arsenal fans, who are thrilled their club acted to quickly and adeptly to snap up one of their targets.
Monreal's name came out of the blue, with rumours beginning at around 4pm on deadline day, with fans who didn't know much about him delighted to learn he is a Spain international.
The bad news is he is cup-tied for the Champions League, but his signing could be crucial in helping them reach the top four and then qualify for the competition next season.
He has taken the number 17 shirt will go straight into the squad for the game with Stoke tomorrow, and is likely to start.
To mark his arrival, Arsenal's official website set up a #WelcomeNacho hashtag for fans to send their messages to the player.
Here's a selection of some of the best...
#WelcomeNacho so happy the Spanish core is getting bigger! Nacho is a vital signing, he will help get us in the top four!
@thevincewood: Arsenal have signed a defender! Let's hope his defending is as crisp and his tackles as crunchy as his name suggests
@nathmobley: Love the slight Spanish feel to the team now. Exactly the kind of player we want. Hopefully see you tomorrow at the stoke game
@nicoafc: Man from Malaga. The savior of our defense? Yes, I think.
@kumailh: If Del Bosque thinks hes good enough then end of story hes good enough for us!
#welcomenacho welcome montreal! i hope that you will help the defence of arsenal to stop the lousy striker of man u.
@kevinliyk: Welcome to Arsenal, Monreal !!!! There's no better way of starting your Arsenal career by getting all 3 points against Stoke!
@nikkip_003: So we sign one player.......... Well at least we don't have to see Santos play at LB
#WelcomeNacho I don't want to sound Cheesy but can't wait for you to Dip straight into the 1st team and make some Crunching tackles!
#WelcomeNacho NACHO NACHO MAN.HE CAME FROM SPAIN TO ENGERLAND. NACHO NACHO MAN HE'S GONNA HELP US BEAT THE GERMANNNS! Welcome to AFC fella!
Are you excited to see Monreal at Arsenal?
image: © lodekka