The following day, IRFU international referee Alain Rolland will be in the middle for the last-four clash of Saracens and Toulon at Twickenham.
It will be Dubliner Rolland's 71st appearance as a match referee in the Heineken Cup, equalling the record set by his good friend and former international referee Alan Lewis.
The all-French Amlin Challenge Cup semi-final between Perpignan and Stade Francais at the Stade Aimé Giral on Friday, April 26 will be refereed by another top-ranking Irish referee, George Clancy from Limerick.
England's Wayne Barnes will be in charge of the second semi-final, a day later, between last season's Heineken Cup Leinster and the reigning Amlin Challenge Cup champions Biarritz Olympique at the RDS.
The Heineken Cup and Amlin Challenge Cup match official appointments were made following a meeting of the ERC Match Officials sub-committee.
The meeting reviewed match official performances across all relevant tournaments in conjunction with feedback from the referee managers in each Union and from club coaching staff.
HEINEKEN CUP SEMI-FINALS:
Saturday, April 27 -
Clermont Auvergne v MUNSTER, Stade de la Mosson, 6pm local time/5pm Irish time
Referee: Nigel Owens (Wales); Assistant referee 1: Leighton Hodges (Wales); Assistant referee 2: Ian Davies (Wales); TMO: Gareth Simmonds (Wales); Citing Commissioner: Douglas Hunter (Scotland)
Sunday, April 28 -
Saracens v Toulon, Twickenham, 3pm
Referee: Alain Rolland (Ireland); Assistant referee 1: Peter Fitzgibbon (Ireland); Assistant referee 2: Andrew McMenemy (Scotland); TMO: Marshall Kilgore (Ireland); Citing Commissioner: Denis Templeton (Ireland)
AMLIN CHALLENGE CUP SEMI-FINALS:
Friday, April 26 -
Perpignan v Stade Francais, Stade Aimé Giral, 9pm local time/8pm Irish time
Referee: George Clancy (Ireland); Assistant referee 1: Dudley Phillips (Ireland); Assistant referee 2: Marius Mitrea (Italy); TMO: Jim Yuille (Scotland); Citing Commissioner: Ian Goodall (Scotland)
Saturday, April 27 -
LEINSTER v Biarritz Olympique, the RDS, 2.30pm
Referee: Wayne Barnes (England); Assistant referee 1: Greg Garner (England); Assistant referee 2: Paul Dix (England); TMO: Geoff Warren (England); Citing Commissioner: Ray Wilton (Wales)