Mats Hummels' switch of allegiance became official on Monday after he was pictured putting pen-to-paper on a Bayern Munich deal.

Hummels was all smiles in Bavaria as he officially signed a five-year contract with the German giants next to club chief Karl-Heinz Rummenigge.

The centre back also posed alongside the latter as he held a Bayern Munich home shirt ahead of next season.

Mats Hummels (left) poses with a Bayern Munich shirt on Monday after joining from Borussia Dortmund

Hummels sits down with Bayern chief Karl-Heinz Rummenigge after penning a five-year deal in Bavaria

The Germany international has become a key member of Dortmund's side since arriving at the club in 2009

MATS HUMMELS THIS SEASON Appearances: 30 Goals: 2 Pass accuracy: 86 per cent Tackles won: 68 per cent Aerial duels won:70 per cent *Bundesliga statistics only Advertisement

Earlier this month, Bayern confirmed the signing of Hummels from Bundesliga rivals Borussia Dortmund for £30million.

The Germany international has long been linked with a return to the club he started his career with before leaving for Dortmund in 2009.

Carlo Ancelotti, who will take over from Pep Guardiola at the end of the season, has boosted his defensive ranks with the signing and the move has been hailed by Rummenigge.

'We're delighted that Mats Hummels has decided to join Bayern,' said the Munich chairman on his club's website earlier this month.

'Mats is one of the best central defenders in the world and we're able to improve the quality of our team even further with him.'

Hummels had one year left to run on his contract at Signal Iduna Park and had informed Dortmund recently of his desire to leave them this summer.

But the defender, who initially joined Dortmund on loan in 2008 before sealing a permanent move the following season, has revealed his emotional attachment towards the club.

'This was not an easy decision for me after eight and a half successful years with BVB,' he told the club's website. 'I was always proud and still am to wear the BVB shirt and to be part of this extraordinary team.'

Hummels, pictured playing against Bayern in March this year, has penned a five-year contract at Allianz Arena

The outgoing Borussia Dortmund captain helped the club win two Bundesliga titles and the German Cup

PLAYERS TO MAKE THE MOVE FROM DORTMUND TO BITTER RIVALS BAYERN Thomas Helmer (1992) The first player to make the jump from Dortmund to Bayern, Germany defender Thomas Helmer caused a major media storm back in 1992. Torsten Frings (2004) Another Germany international who moved from Dortmund to Bayern, Frings' transfer was probably the most cordial. After only two years at Dortmund, Bayern snapped up the midfielder for £7.2m in 2004. Mario Gotze (2013) After several years playing second fiddle to Dortmund, Bayern flexed their financial muscles in 2013 and carried off their biggest transfer coup for a long time, prising Dortmund's brilliant young star Mario Gotze away from their rivals. Robert Lewandowski (2014) Bayern had also tried to sign Robert Lewandowski in the summer of 2013. Determined not to lose their two best players to Bayern in one transfer window, Dortmund turned down all offers, even though they knew that would mean losing Lewandowski on a free transfer. Kit Holden Advertisement

Hummels' final home appearance in Dortmund colours will be against Cologne on Saturday and club chief Hans-Joachim Watzke has appealed to the fans to back their departing captain.

'I would like to stress that Mats behaved very openly and fairly towards us at all times,' he said.

'Mats won two Bundesliga titles with BVB and the double in 2012. He reached the final of the Champions League with us in 2013 and became world champion in 2014 while a Dortmund player.

'We respect Mats' decision and hope that, both for him and BVB, he receives the recognition during his last few weeks for the Black-and-Yellows that he deserves, and that he leaves Dortmund with the DFB-Pokal (German Cup) in his hands.'

Hummels' confirmed move on May 10 came on the same day Bayern announced the signing of 18-year-old Portuguese wonderkid Renato Sanches from Benfica.

Hummels celebrates with the World Cup after helping Germany triumph in Brazil in 2014

The defender was a star member of Germany's World Cup-winning squad and played in final against Argentina

TRANSFER COMPLETE! #FCBayern have also signed @matshummels, with the centre back agreeing a contract until 2021 too! pic.twitter.com/YShoT9dlL9 — FC Bayern English (@FCBayernEN) May 10, 2016

MATS HUMMELS STATEMENT ON TWITTER 'After my transfer to FC Bayern was announced today, I would like to expand on the whole situation slightly more. 'I'm sure as you can imagine the last few weeks have been very nerve-wracking for me, because I have made one of the most difficult decisions in my life so far. In the end, I am beginning to realise, again, a new challenge is upon me in my hometown where my family and many friends live. 'It is clear to me that it will be difficult for some people to understand my decision. But after eight-and-a-half really great years in Dortmund, it was time for me to try something new again. 'With a heavy heart I now leave the club and the team with whom I have grown together, and have been able to celebrate great success with. 'Therefore, I would like to thank all who have contributed to this. With you, the exceptional fans of this great association. All the staff at the club. Also, of course, my three coaches which I have had the fortune to experience here, and Michael Zorc and Hans-Joachim Watzke. 'And particularly my teammates, as they are – regardless of the fact that these last few years without you would not have been possible – always an open ear for me. 'Of course I also thank the many messages, comments and posts, which tried to convince me to stay at BVB. And also the great pep talk after our home game against Wolfsburg, whether in the stadium or in the supermarket, I was very touched by it all. This speaks volumes about the unique BVB fans and I know it is very much appreciated. 'Now I'm going to be in the remaining training sessions and give everything to still play the remaining time with a dignified farewell. With the trophy in the hands back in the pot to come after the finale! 'Thank you! 'Mats.' Advertisement

Sanches has put pen to paper on a five-year deal with the German giants after Benfica agreed to cash in on the teenager in a deal worth an initial fee of £28m.

The Bundesliga champions, who retained the German league title at the weekend, could pay an additional £35m due to several additional clauses inserted into the agreement between the clubs.

Hummels' move to the Allianz Arena was confirmed less than an hour later by both German clubs. He helped Dortmund win two Bundesliga titles and the German Cup.

He was also part of Jurgen Klopp's team who finished runners-up in the 2013 Champions League final where they were beaten by Bayern at Wembley.

Bayern's relationship with Dortmund was frayed by the transfer of Mario Gotze in the summer of 2013 and Robert Lewandowski's move in the same direction the following year.

Hummels made the permanent switch to Dortmund in 2008 after only one first-team appearance for Bayern

The defender, pictured with Jurgen Klopp in 2012, will be reunited with Robert Lewandowski (left) at Bayern

Carlo Ancelotti, who will take over the reins from Pep Guardiola this summer, has boosted his defensive ranks

Bayern have also announced the signing of Renato Sanches from Benfica for £28m