Here are the seven European clubs to have achieved the feat:
2012/13: Bayern Munich (won the Champions League, Bundesliga, German Cup and German Super Cup)
2009/10: Inter Milan (won the Champions League, Serie A, Coppa Italia)
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2008/09: FC Barcelona (won the Champions League, La Liga, Copa del Rey)
1998/99: Manchester United (won the Champions League, English Premier League, FA Cup)
1987/88: PSV Eindhoven (won the European Cup, Eredivisie, KNVB Cup)
1971/72: Ajax Amsterdam (won the European Cup, Eredivisie, KNVB Cup)
1966/67: Celtic (won the European Cup, Scottish League Championship, Scottish Cup, Scottish League Cup)
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