The 23-year-old, who helped Fortuna to a sixth-placed finish in the second tier this season, has put pen to paper on a four-year contract and will join up with his new team-mates when the 2014/15 season begins on 1 July.
"Fabian Giefer is a very ambitious young goalkeeper with a lot of potential,” commented the Royal Blues’ sporting director Horst Held. “We are delighted that he has chosen to join the club.”
After coming through the youth ranks at Bayer 04 Leverkusen, Giefer moved to Düsseldorf in 2012, playing every minute of Fortuna’s first campaign in the Bundesliga for 15 years in 2012/13, at the end of which the club were relegated last summer. He made 30 appearances for die Flingeraner this term but was unable to help the club secure a return to the top flight.