Manchester City have signed German international defender Jerome Boateng from Hamburg for an undisclosed fee.The 21-year-old, who has signed a five-year deal, will officially become a City player on 1 July. [LNB]Boateng was in Manchester on Saturday to confirm the details before he flies to South Africa to join the German national team for the World Cup. [LNB]"He is a young player who is already of a very high quality," City boss Roberto Mancini told the club's website. [LNB]"I think he can continue to improve at City. He can play a number of positions in defence, which is important. [LNB]"He has proved his ability in Germany and I think he can be a very important player for Manchester City in the Premier League."[LNB] What are your thoughts on the signing? Marton Fulops Monster Boateng started his career with Hertha Berlin before moving to Europa League semi-finalists Hamburg in 2007 and is the younger brother of Portsmouth midfielder Kevin-Prince Boateng. [LNB]The brothers could end up playing each other at the World Cup as the Pompey player has elected to represent Germany's Group D rivals Ghana. [LNB]And Mancini added: "It's good for Jerome to have agreed terms ahead of the World Cup, so he can now concentrate on playing for Germany. [LNB]"I will be very interested to see how he gets on in the tournament, before welcoming him back to meet his team-mates in pre-season." [LNB]Boateng follows current City players Vincent Kompany and Nigel de Jong in moving to Eastlands from Hamburg.