Southampton have signed Denmark defender Jannik Vestergaard from Borussia Monchengladbach.
The 6ft 6ins centre-back, 25, has agreed a four-year deal with the Premier League outfit.
Vestergaard, who has played in both the Champions League and Europa League, is relishing the challenge of the English top flight.
He said on Southampton's website: "I knew of the interest before the World Cup and the club has followed me for quite some time and done a lot of scouting, which is also a good sign for me that they know my strengths and weaknesses.
"The degree to which the club wanted me was important in my decision. They had done a lot of research, seen a lot of live games and on video as well. I feel I'm at a really good place to develop."
Southampton have omitted big-money stars Guido Carrillo and Sofiane Boufal from their pre-season tour of China.
The two high-profile forwards' St Mary's futures now appear in doubt, after boss Mark Hughes opted not to include them in a 30-man travelling party.
Saints' main group headed out to the Far East on Saturday, with new signing Mohamed Elyonoussi set to join the tour in due course.
Southampton will take on Bundesliga runners-up Schalke and Chinese side Jiangsu Suning as part of the Club Super Cup.
"I'm quite excited and the majority of the guys understand exactly what I want, what my standards are and what I am asking them to do," Saints boss Hughes told the club's official website.
"We are looking forward to it, there's some good quality games within the two weeks
"The point is to get the majority of the guys back and we've got a few new faces as well, so that's always good to be together as a group for a certain length of time. It helps new guys to integrate.
"So we've got the benefit of a good three, four months work, going into the new season."
Carrillo only joined Southampton from Monaco in January, in a £19million club-record deal.
The Argentinian forward was scoreless in 10 appearances however, and struggled to acclimatise as Saints laboured under manager Mauricio Pellegrino's troubled tenure.
Boufal joined Saints in 2016 in a then club-record £16million deal, arriving from Lille under some fanfare from then-Saints boss Claude Puel.
The Morocco forward has been another to produce indifferent Premier League form, though, and now it appears both men are on the extremities of new boss Hughes' long-term plans.
Southampton have signed Norway forward Mohamed Elyounoussi from Swiss club Basel on a five-year deal.
The 23-year-old, born in Morocco, scored 23 times in 83 appearances for the Swiss Super League side.
Southampton manager Mark Hughes said on the Premier League club's website: "Mohamed is clearly another very exciting addition to our attacking options."
Elyounoussi had a spell in Norway with Molde, and the 16-cap international brings with him experience of both the Champions League and Europa League.
Press Association Sport understands the transfer fee to be worth in the region of £16million.
Saints boss Hughes added: "He's still at a young age as well, so we're confident he can continue to improve and fulfil even more of his potential with us.
"Following on from the arrival of Stuart Armstrong this week, we feel we have made real progress in adding a new dimension to our attack ahead of the season."
Elyounoussi added: "I'm really happy to be here and I am really excited to get started.
"The club have been following me for a long time, watching many games, so I feel really confident to come here and to get even better and develop myself."
Southampton midfielder Dusan Tadic has joined Dutch side Ajax for an undisclosed fee, the Premier League club have announced.
Serbia international Tadic, 29, scored 23 goals in over 160 appearances during a four-year spell with Southampton.
"Southampton Football Club can confirm that Dusan Tadic has agreed a move to Ajax for an undisclosed fee," Saints confirmed on their official website.
"The transfer, which will be officially completed on July 1, sees the 29-year-old move back to the Dutch top flight, four years after joining Saints from FC Twente."
Tadic has started in both of Serbia's World Cup group games in Russia and played the full 90 minutes in last week's 2-1 defeat to Switzerland.
Southampton signed him for £10.9million in July 2014 from Twente, who paid over £6m to lure him from Groningen four years earlier.
He was instrumental in helping Southampton to their sixth-placed finish in the Premier League in 2016, starring alongside Graziano Pelle and Sadio Mane, and was the club's joint top-scorer last season with seven goals.
Southampton have announced defenders Jeremy Pied and Florin Gardos will leave the club at the end of their contracts.
Pied joined the Saints from Nice in August 2016, but made only eight appearances after being hampered by a long-term knee injury.
Romanian centre-back Gardos, meanwhile, departs following a loan spell back in his homeland at Clubul Sportiv Universitatea Craiova, having signed for Southampton in 2014.
Southampton last week confirmed manager Mark Hughes had agreed a new three-year deal, after helping to keep the club in the Premier League.
Mark Hughes has been rewarded for keeping Southampton in the Premier League with a new three-year deal.
The former Wales, Manchester City and Stoke boss was tasked with keeping the Saints in the top flight when he took charge in March.
He did just that and will now stay at St Mary's - along with assistants Mark Bowen and Eddie Niedzwiecki - until the summer of 2021.
"Mark, Eddie and I are thrilled to have signed long-term contracts with the club. It was the only option we considered, having spent the last eight weeks with the club," Hughes said.
"Now it is vital that we take the unbelievable support we received from the fans during the last few games into next season.
"The staff and the players will work hard every day to deliver the success this club deserves, and with everyone pulling together we will achieve our goals."
Mark Hughes would "love" to continue as Southampton manager after masterminding Premier League survival.Read the full story ›
Southampton have written a one-star review for the hotel which cancelled their booking ahead of the crucial game against Swansea.Read the full story ›
Southampton took a huge step towards safety as a 1-0 win at Swansea inched their Welsh rivals towards the Premier League trapdoor.Read the full story ›