Complex sentence: Following the conclusion of the 2009--10 season, his second year with Astana, Letowski announced his retirement and returned to where he began his career with the Sting, taking up an assistant coaching role on April 17,2010.
Split into simpler sentences: Following the conclusion of the 2009--10 season, his second year with Astana, Letowski announced his retirement. Letwoski returned to where he began his career with the Sting, taking up an assistant coaching role on April 17,2010.