Saints have confirmed the signing of Virgil van Dijk on a five-year deal, for a fee which could rise to £13m.

The Dutch centre half has become the club’s most expensive defender after Saints sealed the deal with Celtic for his services.

Saints have been keen to sign for Van Dijk for over a year, but Celtic have been reluctant to let one of their key men depart.

They have eventually relented this summer after failing to qualify for the group stages of the Champions League, and have accepted a deal believed to be worth an initial £11m rising to a possible £13m.

Van Dijk said: “I’m delighted. It was a very easy decision to join this club. 

“This is a very ambitious club, who have been doing very well in the last couple of years. It’s a great place to be and it’s the right step for me.

“For me now to get the opportunity to play in the Premier League is unbelievable and I will enjoy it.

“I know it’s an ambitious club – they have been through a lot throughout the years. They are trying to play football and that’s something that really attracted me.

“I’m so excited. I hope to settle in really quick, get everything around football sorted, start playing and enjoying it because the most important thing in football is to have fun and enjoy every day.”

Van Dijk, 24, started his career at Willem II, but got his first break as a professional at FC Groningen, the hometown club of Ronald Koeman.

After a little more than two impressive seasons in the first team, Celtic paid £2.6m to take him to Scotland in 2013.

He made more than 100 appearances for Celtic in just over two seasons at the club, won a Player of the Season award and was part of the record breaking defence that went 1,215 minutes without conceding a goal.

He also won two league titles and a League Cup with the Scottish giants.

Van Dijk now has Jose Fonte, Steven Caulker and Maya Yoshida for competition as he seeks to establish himself as a first team regular at Saints.

Executive Director of Football Les Reed said of the deal: “We’re delighted to have finally got Virgil into the club after long and lengthy negotiations.

“We’ve had Virgil in our system for a long time and have explored the possibility of signing him in previous transfer windows, and this year we had a really strong opportunity to do it.

“The Champions League had an effect on the moment of release, which we were aware of, so it was about keeping our focus and doing our due diligence before eventually getting him over the line.

“He’s still a young man but a very mature young man who has played a very good level of football at Celtic and in Europe. He’s had an excellent upbringing and still has a lot of time ahead of him.

“Virgil has signed a long-term contract, so clearly sees a strong future here with us. He’s young, hungry and wants to prove himself.”