Exeter Chiefs will face the Heineken Cup champions for the second successive season after they were drawn with Toulon.
Castres claimed a shock 19-14 win over Toulon to win the Top 14 title and deny their opponents from doing the double.
Toulon stand on the verge of an historic Euro-French double as they face Castres in the Top 14 final on Saturday.
Castres will face Toulon in the Top 14 Final after claiming a shock 25-9 victory over Clermont in in Nantes.
Clermont are looking to bounce back from Heineken Cup defeat as they take on Castres for a place in the Top 14 final.
Castres booked their place in the Top 14 semi-finals after a 22-12 victory over Montpellier at Stade Pierre-Antoine.
A losing bonus point for Montpellier in Bayonne was enough to eliminate Perpignan from the race for the play-offs.
Toulouse have confirmed the signings of Joe Tekori, Jean-Pascal Barraque and Yacouba Camara for the 2013/14 season.
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