The Ajax star has completed a switch to St James's Park from the Eredivise champions, while the France international has emerged as a transfer target for Serie A side NapoliNewcastle have announced the signing of Siem de Jong for an undisclosed fee, with the Ajax captain a potential replacement for Moussa Sissoko, who wants to leave St James's Park.
De Jong has playeed over 150 league matches for the Eredivisie champions and becomes Alan Pardew's first signing of the summer, having agreed a six-year contract.
"It is great to have signed for Newcastle," he told the club's official website. "It is a big club which my brother [Luuk de Jong] told me all about so I already feel good here.
"I had been at Ajax a long time and wanted a new challenge in a new environment and a new country. Coming to Newcastle is a great opportunity and the chance to play for a club like this in the Premier League was one I could not turn down.
The Dutchman missed out on a place in Louis van Gaal's Netherlands squad for the World Cup but could be set to replace France international Moussa Sissoko in the North East.
Sissoko could be on the way out after a little over a year on Tyneside, with Serie A club Napoli a potential destination for the former Toulouse man.
The 24-year-old, who is part of the France squad at the World Cup and scored as Didier Deschamps's side smashed Switzerland 5-2 in their second group game, is seen as a realistic target for Rafael Benitez's team.
Goal understands that the Italian club would be willing to nearly double Sissoko's wages, while the lure of Champions League football is likely to be another factor in any potential negotiations.
With Sissoko contracted until 2019, however, Newcastle will not be forced to sell one of their prized assets on the cheap and will be looking to recuperate at least the fee that they paid to bring the Frenchman to England back in January 2013.