Despite a red card for Steff Evans the Scarlets pulled off a major shock in Dublin
They became the first side in history to win a PRO12 semi-final away from home
Ospreys were the last Welsh club to win the competition in 2012
Scarlets produced a historic performance to beat Leinster in the Pro12 semi-final despite having winger Steffan Evans sent off before half-time.
The winger was red-carded for a tip tackle on centre Garry Ringrose in the 38th minute when Scarlets were leading 21-10.
Evans, back-row Aaron Shingler and scrum-half Gareth Davies scored fine tries for the visitors.
Centre Ringrose and number eight Jack Conan touched down for the home side but it wasn't enough, meaning they miss out on the 27 May final in Dublin.
The victory will without a doubt go down on the honours board at Parc y Scarlets alongside even the legendary victories against New Zealand and Australia.
Following the win, Scarlets coach Wayne Pivac has taken a veiled swipe at the Wales management for continually ignoring flanker James Davies, who starred in what was probably his best performance to date.
"I have said from day one he is a fantastic player. I rate him very highly," said the New Zealander.
"His performances over three seasons now, not one or two weeks like some of the other players, have been top drawer.
Leinster: 15 Joey Carbery, 14 Adam Byrne, 13 Garry Ringrose, 12 Robbie Henshaw, 11 Isa Nacewa (c), 10 Johnny Sexton, 9 Luke McGrath, 8 Jack Conan, 7 Josh van der Flier, 6 Rhys Ruddock, 5 Hayden Triggs, 4 Ross Molony, 3 Tadhg Furlong, 2 James Tracy, 1 Jack McGrath Replacements: 16 Richardt Strauss, 17 Cian Healy, 18 Michael Bent, 19 Devin Toner, 20 Dan Leavy, 21 Jamison Gibson-Park, 22 Ross Byrne, 23 Zane Kirchner
Scarlets: 15 Johnny McNicholl, 14 Liam Williams, 13 Jonathan Davies, 12 Scott Williams, 11 Steff Evans, 10 Rhys Patchell, 9 Gareth Davies, 8 John Barclay (c), 7 James Davies, 6 Aaron Shingler, 5 Tadhg Beirne, 4 Lewis Rawlins, 3 Samson Lee, 2 Ryan Elias, 1 Rob Evans Replacements: 16 Emyr Phillips, 17 Wyn Jones, 18 Werner Kruger, 19 David Bulbring, 20 Will Boyde, 21 Jonathan Evans, 22 Hadleigh Parkes, 23 DTH van der Merwe
Date: Friday, May 19 Venue: RDS, Dublin Kick-off: 19:45 BST (18:45 GMT) Referee: Marius Mitrea (Italy) Assistant Referees: Mike Adamson (Scotland), Simone Boaretto (Italy) TMO: Alan Falzone (Italy)