Saints have completed the signing of Juanmi from Malaga for a fee of €7m.
The club had the opportunity to sign the player for just €7m due to a clause in the player's contract.
Juanmi has scored 20 goals in 93 appearances for Malaga since making his debut as a 16-year-old in 2010, as well as winning the U19 European Championship with Spain in 2011 and 2012.
He had been linked with Aston Villa, Newcastle United and Real Sociedad, but has opted to make St. Mary's his home, today signing a four-year deal to join Ronald Koeman's ranks ahead of the new season.
He will now return to Spain, before reporting for pre-season training on the 29th of June.
Speaking after making the move to Saints, the Spanish forward said:"It's a pleasure to be here and I am looking forward to being a part of this club.
"I am anxious and I want to start as soon as possible. This is a big club and it has shown a lot of trust in me.
"The training ground is magnificent and likewise the stadium. It really, really is a big club.
"Since I was very young, it's always been a dream for me to play in the Premier League. The style of football played here is similar to the way I play, so it's a dream come true.
"Now I just want to start playing and to start scoring goals."
To find out more about Southampton's newest recruit, check out our interview with Spanish journalist Alberto Alvarez from last night.