He has the distinction of being the only one of the two boys who
appeared on
Irwin Allen's TV series to be doubled. He and
Bill Mumy were the only boys to appear in Allen's series, and
Mumy had the distinction of being the only one of the two boys to
appear as his past self (in the
Verschollen zwischen fremden Welten (1965) episode,
"Project: Earth"), in a flashback to the time of the Jupiter Two's
original launch. But Stefan had to be doubled in the
Planet der Giganten (1968) episode,
Wild Journey (1970), because he
had already gone into puberty and thus could not appear as his younger self.
