Newcastle United secured the signing of Dan Burn late on Monday night.
The centre-back has left Brighton in a deal worth €15million.
Burn is Newcastle's fifth signing of the January window, following the arrivals of Chris Wood, Kieran Trippier, and Bruno Guimaraes.
Matt Targett has also joined on loan from Aston Villa until the end of this season.
Centre-back was one area that Newcastle manager Eddie Howe desperately wanted to strengthen this window, and he's done just that with the in-form Burn.
“We were not actively looking to sell Dan during this window, but the transfer represents a very good transfer for our club and the player.
“Newcastle are Dan’s boyhood club," Brighton boss Graham Potter revealed, "and this move allows him to potentially play out the rest of his career at his home club.
“Ever since I have been at the club, Dan has been brilliant for me. He is a superb professional, adaptable and a great character on and off the pitch.
“We will miss him here, but we understand his reasons for wanting to move and he goes with our thanks and very best wishes for the future.”
Burn's departure is likely to open the door for Republic of Ireland defender, Shane Duffy. He's currently laid up with an ankle injury, but can expect more game time than he had been receiving this season once he returns.
Howe said: "I'm delighted to bring Dan back to the North East. He knows exactly what it means to represent this club and he will be a big presence for us on and off the pitch.
"We have been very keen to add competition defensively and Dan fits the profile we have been looking for. He is naturally left-footed, which provides further balance to our backline, and he will be a great addition to the group."