[2] In August 1167, Duke Frederick IV of Swabia died on an Italian campaign.
It can be assumed that Frederick V was bypassed from the royal succession because he had a weak constitution since birth and wasn't expected to survive infancy.
[3] Two medieval sources confirms that Frederick V was still alive when his brother was elected King of the Romans.
[4] Since his fiancée Eleanor was married to King Alfonso VIII of Castile in 1170, is assumed that he died in mid-1169 or early 1170.
[4][7] Since Otto, the next son of Barbarossa born after Conrad/Frederick VI, was probably born during June–July 1170,[8] Frederick V must have died some time before, otherwise the rather unusual renaming of Conrad would have been without purpose, because the Emperor could simply have called the next son Frederick (instead of Otto).