[1] Mildenberger lost his first fight for the European Heavyweight title when he was knocked out by Welsh boxer Dick Richardson in one round in April 1962.

Later that year, Mildenberger scored a first-round knockout over Sante Amonte to capture the European Heavyweight title.

Years later, Angelo Dundee said a tenth round punch to the liver area hurt Ali, whose ability to withstand body blows was legendary.

[3] In 1967, Mildenberger participated in a tournament staged by the World Boxing Association to determine the new heavyweight champion after Ali was stripped of the title for refusing induction into the US military draft.

Subsequently, in September 1968, Mildenberger's career ended when he lost the European Heavyweight title to Henry Cooper by eighth round disqualification after headbutting his opponent.