Borussia Dortmund announced the signing of Nico Schulz from fellow Bundesliga side Hoffenheim for a reported €25million fee.
Dortmund fell short in its bid to unseat Bundesliga champion Bayern Munich but has moved quickly to add to its squad for 2019-2020.
Schulz has broken into the Germany team since swapping Borussia Monchengladbach for Hoffenheim in 2017 and feels joining Dortmund is a natural next step.
"Borussia Dortmund are a top club whose team plays a football that simply suits me and my style, and I think I can help the team with my way of playing and we can achieve great things together," he said. Schulz, 26, will be reunited with a familiar face in Dortmund as he played under head coach Lucien Favre at Gladbach.
"Nico Schulz is a defensive player who has made another leap in performance over the past few years and, like the German national football team, we will benefit greatly from his physique, his pace and his extreme dynamism," Dortmund sporting director Michael Zorc added.
Schulz becomes the third biggest sale in Hoffenheim's history, although neither club disclosed the fee, behind Roberto Firmino and Kerem Demirbay who joined Liverpool and Bayer Leverkusen respectively.
"Even though we agreed to the transfer at the end after weighing all the circumstances, of course we regret the loss of Nico," said Hoffenheim's director of football, Alexander Rosen.
"He has made a sensational development in just two years and is symbolic of the way players can improve at TSG."
Schulz, meanwhile, is grateful for the part Hoffenheim played in his rise over the past two seasons.
"I know very well what I owe to TSG Hoffenheim, the people here in the club, the coaching staff, the fans and my team-mates," he told the club's official website.
"That's why I've been thinking about the change for a long time and, now I've chosen this path, I'm grateful to TSG for agreeing to the transfer."