The Arms Park youngsters will start the game as favourites after defeating the Welsh All Blacks in two league clashes and Cardiff secured the league title last weekend after their 26pts to 20 win over Bridgend.
Neath are battling for the runners up position but will be looking to deny the Arms Park side an unique league and cup double in the competitions inaugural final.
Ryan Williams starts at scrum half partnering Dylan Pugh, who contributed so effectively to the semi-final success away to Pontypridd. Wing Andrew Jones returns while the pack remains unchanged.
Cardiff show just two changes from the side which defeated Llanelli in the last round with Darren Ryan selected at centre and lock Tait returning to the side after his recent run in the senior side.
Neath U'21s: P.Thomas, R.Carter, M.Jones, P.Smiriglia, A.Jones, D.Pugh, R.Williams, P.James, A.Matthews (capt), A.Jones, G.Evans, L.Bassett, S.Peters, D.Evans, S.Phillips
Cardiff U'21s: C.Anderson, E.Jones, O.Ashman, D.Ryan, G.Williams, N.Macleod, C.Miller (capt), J.Yapp, K.Jarma, D.Evans, L.Tait, C.Stamatakis, J.Malpas, M.Leach, M.Leaman
Welsh players and management joined Deputy Minister for Sport Ken Skates at the Pierhead Building, Cardiff Bay earlier this week to reveal the Union's pioneering school-club hub initiative has been so successful the project will now almost double the scale of the original project.
The Scarlets, Newport Gwent Dragons, Cardiff Blues and the Ospreys look ahead to Judgement Day III which sees the Blues take on the Ospreys (2.30) and the Dragons tackle the Scarlets (4.45pm) at the Millennium Stadium tomorrow afternoon.
Ystradgynlais and Ynysddu played out a titanic struggle at Taffs Well in the SSE SWALEC Bowl semi-final. At the end of the game neither team could be separated after a 15-15 stalemate but Ystradgynlais go through on try count.
Blues strike first in JD III battle - Newport Gwent Dragons lock Andrew Coombs, WRU referee Dylan Llyr Jones and Cardiff Blues hooker Matthew Rees decide dressing room allocations for Judgement Day III
Wales Under 18 captain Calum Haggett has received a conditional offer to read Biomedical Science at St Anne's College, Oxford. WRU chairman Gareth Davies went to meet Calum and Coleg y Cymoedd Principal Judith Evans to wish him luck in his exams and pass on some of his personal experience.
Dodgy tattoos, carthorses, Avatar and soft chins are revealed by Wales Sevens players Tom Williams and Sam Cross as they profile the Wales Sevens squad taking part in Hong Kong this weekend in the latest round of the HSBC Sevens World Series.