 Despite not participating in the 1979 European Cup Final at the Olympiastadion, in which Forest beat Malmö FF 1–0, Mills became the youngest player to win the European Cup at the age of 17 years and 201 days on the virtue of having made one appearance in the competition that season.He finished the 1978–79 season, in which Forest were First Division runners-up, with six appearances and one goal.Due to an injury to Trevor Francis he started in the 1–0 victory over Hamburger SV in the 1980 European Cup Final, staged at the Santiago Bernabéu Stadium, and being aged 18 meant he became the youngest player to appear in a European Cup final.