 Complete the following phrase:  In 2008, he moved with Klopp to become assistant manager at Borussia Dortmund. Described by Klopp as his right hand, Buvač helped lead Dortmund to back-to-back Bundesliga wins in 2011 and 2012, as well as the DFB-Pokal in 2012, the DFL-Supercup in 2008, 