Premier League champions Chelsea have signed Germany defender Antonio Rudiger from Roma on a five-year contract for an initial fee of £29m.
Rudiger, 24, completed the transfer one week after helping world champions Germany win the Confederations Cup.
"It's a great feeling because not every player has the opportunity to join a huge club like this," said Rudiger.
The fee for Chelsea's first major signing of the summer could rise to £33.3m with add-on clauses.
"Antonio is still young but is experienced at club and international level and possesses all the requisite attributes to thrive in the Premier League," said Chelsea's technical director Michael Emenalo.
"He is a player of proven quality."
Rudiger will wear the number two shirt left vacant after Branislav Ivanovic's departure to Zenit St Petersburg in February.
Because he was set to take a break after his involvement in the Confederations Cup, Rudiger is unlikely to be involved when the majority of Antonio Conte's squad return to pre-season training on Monday.
The rise and rise of Antonio Rudiger
Rudiger played for Borussia Dortmund at youth level before moving to Stuttgart in 2011.
He made his Bundesliga debut in January 2012 and clocked up 66 appearances in Germany's top flight before moving to Roma in 2015.
Rudiger made 30 Serie A appearances in 2015-16 as Roma finished third and a further 26 in 2016-17 as they were runners-up to Juventus.
He also played six Champions League games in 2015-16 as Roma reached the last 16.
'Dad, I want Rudiger!'
Chelsea continued a summer trend among Premier League clubs by announcing the signing with an elaborate video on their Twitter feed.
In the video, a young boy visiting Chelsea's club shop asks his dad for a shirt with Rudiger's name on the back.
His dad tells him he cannot have the name of a player Chelsea have not signed and recommends David Luiz or Eden Hazard instead.
"Dad, I want Rudiger!" says the boy, to which the shop assistant goes into a stock room and asks the player, wearing a number two Chelsea shirt, if that's OK.
"No problem," he says. "I'm a Chelsea player now."
Mani Djazmi, BBC World Service reporter
Like his inexperienced team-mates, Antonio Rudiger grew into the Confederations Cup. By the time of Germany's victory, he looked a seasoned international in a team whose players' mutual understanding seemed flawless.
He was strong and composed in the German defence which, like Chelsea's under Antonio Conte, featured three central defenders, although Rudiger can also play at right-back.
In the final, as Chile's relentless, marauding attackers tested Germany's defensive nerve, he stayed strong, not least when an impeccably-timed challenge denied Charles Aranguiz in the early stages.
It's not often that football managers commit to direct comparisons of players, but Germany coach Joachim Low has likened Rudiger to Bayern Munich's Jerome Boateng.
Rudiger will be hoping that his assured performances at the tournament will help him earn a place alongside Boateng and Mats Hummels at the 2018 World Cup.
But the 24-year-old's history of knee operations - he has had three - along with his eight yellow cards and two reds in all competitions for Roma last season, and his self description of being a hard tackler suggests he will not always be available for Conte.
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