Apart from all the gay-oriented videos he has made even at bodybuilding competitions he always seems to play with homoeroticism a lot, his performances are never innocent or lacking in homoerotic appeal.
I know he has a girlf and, while I don't know if he is actuall heterosexual at least it looks like he likes to be an object of homosexual desire.

German bodybuilders seem to deal better with their collegues engaging in gay-oriented stuff than bodybuilders in the US…

Youtube Video