The player had been linked with a move to Manchester United for the past month, with plenty of reports suggesting the player has agreed a move to the Old Trafford club, but when Bayern Munich coach Pep Guardiola declared his interest in the player the deal was completed days after.
When asked why he chose Bayern, Thiago told the club's official website: "On the one hand, there's the history of the club, which has been one of the best in the world for many years. On top of that, this team plays very attractive football. And I believe the arrival of Pep Guardiola will provide an additional boost."
The player wanted the move to join up with his old boss after recently struggling for games, with the likes of Cesc Fabregas, Xavi and Andres Iniesta.
Thiago dded: "We've known each other for a long time and he's a coach who has placed great faith in me. I'm a huge fan of the way he likes football to be played.
"There aren't many coaches in the world with his ability. He was definitely one of the important reasons for me making the move to Munich."
The deal took place just a few days after Guardiola announced Thiago was his number one target - and claimed it was the Spanish starlet or nobody.
"We're delighted we've successfully negotiated this major transfer," said Rummenigge. "Only recently, Thiago was named best player at the Under-21 European Championship. He's a fantastic player with huge potential, and he will make FC Bayern stronger."
Thiago gained a lot of interest after the performance he put at the European U21 Championships, with the new Bayer Munich midfielder scoring a first-half hat-trick in the final.
"I'm really looking forward to it and I'm extremely happy," he added. "If there's a day in your life when you can be completely happy, today is one of those days. I'm thrilled to be at a massive club like Bayern Munich.
"Munich is a spectacular city with fantastic flair and a tremendous passion for football. I'm really enthusiastic about this adventure. I hope I play plenty of games, and that we can retain the trophies from last season."
Thiago was said to be a major target for Manchester United's David Moyes, but it seems the Manchester United manager has switched his attention to Thiago's former team-mate Cesc Fabregas, with a reported £25m bid lodged yesterday.
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