During his captivity in a Danish prisoner-of-war camp, he met a guitarist named Ladi Geisler, with whom he soon formed a small combo.
Signed to the Polydor label in the 1950s, as a composer, producer and musician he made accordion and dance band music under his own name.
He also started with Middle & South America music recordings under the alias of Roberto Delgado, and with piano albums as Mister Pepper.
The Delgado albums became popular in Europe, and then found an audience in the UK, Japan and North America and Australia as Polydor opened up several international subsidiaries.
Horst made several albums with great international singers including Conny Froboess, Wencke Myhre, Katja Ebstein, Daliah Lavi and Freddy Quinn.