It is unbelievable because this isn’t true.
Franco had a problematic relationship at best with the German Fuhrer.
Hitler and Franco had a summit in 1941, Germany wanted passage for its army through Spain to capture Gibraltar.
The short story was that it never happened. Hitler remarked afterwards that he would rather have his teeth pulled out one by one than to deal with that “impossible man” (Franco)
Germany did help Spain fight off the attempted Communist Revolution in the 1930’s, and Soviet Russia was on the other side. But Spain was not a backer of Germany, and maintained its neutrality during the 2nd world war.