Tottenham have announced the signing of Belgium international defender Toby Alderweireld from Atletico Madrid.
Alderweireld, 26, has signed a contract at White Hart Lane that runs until 2020.
SIGNED: We are delighted to announce the signing of @AlderweireldTob from Atletico Madrid. #WelcomeToby pic.twitter.com/CTThyOs7V7
- Tottenham Hotspur (@SpursOfficial) July 8, 2015
A statement on Atletico's official website added: "Atletico de Madrid and Tottenham Hotspur have reached an agreement for the transfer of Toby Alderweireld to the club from White Hart Lane.
"The Belgian defender expressed his wish to our club of playing with Tottenham this season and the two clubs have finalised the transfer of the fullback to the Premier League team."
Southampton, who had the player on a temporary deal last season, believed they had signed the player after exercising a permanent option in the loan contract.
However, Spurs have now announced that he has moved to White Hart Lane, and the defender told their official website: "I'm very proud to become a Spurs player.
"I'm very happy to be here and I hope to have a wonderful time with this team. From the beginning I knew a lot about [the club] from Jan Vertonghen, Mousa Dembele and Nacer Chadli.
"It's a big club and it's always been a dream to play at a club like Spurs. Now that dream is coming true so I'm very happy, very proud and I will give my best."
"I know the players from the national team and I played with Jan at Ajax, we had a central defensive partnership. It's nice when you join another club that you know a couple of players. I hope to get to know them a little better now."
EXCLUSIVE! Hear from new signing @AlderweireldTob on Spurs TV. Watch - http://t.co/JdtyCiY7NC #WelcomeToby https://t.co/uJuiQpfU94
- Tottenham Hotspur (@SpursOfficial) July 8, 2015
He added: "There is a lot of quality in the team and good, young players the club also wants to develop. Those two games were very tough for us, Spurs had a very good team. "I'm really looking forward to helping the team reach the goals we will set."
It had previously emerged that Atletico had failed to pay the £1.5 million required to cancel the £6.8m buy-out clause included in his loan arrangement with Southampton before the deadline stipulated in the deal.
Saints boss Ronald Koeman said this week: "Southampton signed the option for the player and Atletico Madrid is trying to buy back the option.
"In our knowledge it is and was too late. What happened with Tottenham in the middle I don't know. Seriously, I don't know. [Head of football development] Les Reed is working on that situation. I wait for more news on that situation with Toby."
As Southampton believed they were entitled to sign Alderweireld, the club could consider legal action against Atletico.