England defender Kieran Trippier became Newcastle's first signing under their new Saudi owners on Friday after completing his move from Atletico Madrid, with more arrivals expected in the January transfer window.
The full-back has moved back to the Premier League for an undisclosed fee, understood to be in the region of £12 million ($16 million) plus add-ons.
The former Tottenham defender has signed a two-and-a-half-year contract and his arrival signals the launch of a new era under Eddie Howe, who was appointed as manager at St James' Park in November.
"Newcastle United are delighted to confirm the signing of England full-back Kieran Trippier from Atletico Madrid for an undisclosed fee," the club said in a statement.
"The 31-year-old has agreed terms on a two-and-a-half-year deal and becomes the first senior signing under the club's owners and head coach Eddie Howe."
Speaking at his pre-match press conference, Howe insisted Trippier had not joined the club for financial reasons, and is hoping his arrival paves the way for others to join.
"Kieran hasn't come for the financial benefits of the contract," said Howe, whose team host English third-tier side Cambridge United in the third round of the FA Cup on Saturday.
"He's come for the club and for the challenge that the team faces at the current time, but also the longer-term vision, so I think that's a massive thing for the football club.
"Hopefully with his signing, other players around the world will potentially look at that and share his dream and his vision for what he sees. That's a big thing for us."
Trippier, who was signed by Howe in 2012 for former club Burnley during his spell in charge at Turf Moor, won La Liga with Atletico last season but is relishing his return to England.
"I'm so happy to be joining Newcastle," he tweeted. "Everyone knows the fans are unbelievably passionate and I will give my absolute all for them. I can't wait to get to work."
Newcastle, who have not won a major trophy since 1969, face a struggle just to stay in the Premier League. They are one place off the foot of the table after a single win in 19 games.
But three months after a controversial takeover by the Saudi sovereign wealth fund was given the green light by the Premier League, the club have the chance to splash their new-found wealth in this month's transfer window.
Defenders were expected to be top of the shopping list after Newcastle shipped a Premier League record 80 goals in 2021.
Injuries to Newcastle's two most potent attacking weapons, Callum Wilson and Allan Saint-Maximin, have led to speculation over forward signings, with Arsenal's out-of-favour Pierre-Emerick Aubameyang linked with the club.
Howe confirmed on Friday that Wilson was to undergo a further scan on a calf injury and the results could determine whether or not he needed to sign a player as cover.
"Those results will possibly impact what we do, but it's all dependant, of course, on who's available and who we can recruit because it's probably the toughest position at any time of the year to recruit in," he said.
"The quality of players in that position really is very short on the ground."