Giesen teamed up with Stefanie Frohberg in April 2009. They decided to train in Berlin, coached by René Lohse. Competing in the 2009–10 ISU Junior Grand Prix series, Frohberg/Giesen placed fourth in Lake Placid, New York, and then fifth in Dresden, Germany. After winning the national junior title, they were sent to the 2010 World Junior Championships in The Hague, Netherlands. They finished 11th after placing 9th in the compulsory dance, 15th in the original dance, and 11th in the free dance.