Eurosport - Nathaniel Clyne in action for Crystal Palace, April 2012 (PA Photos)
The 21-year-old England Under-21 international has signed a four-year deal with the Premier League newcomers.
"I'm overwhelmed, really," Clyne told the club's official website.
"As soon as I heard that Southampton were in for me, I was happy and I knew that this was the place where I could try to improve my football, further my career and get a chance to play in the Barclays Premier League."
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