The Arms Park side established an early 10pts to nil lead but the home side battled back to lead 20pts to 10 midway through the second half. However with the introduction of influential fly half Nick Macleod, the Arms Park youngsters levelled with two tries scored in quick succession and Macleod added a late penalty and drop goal to secure both the win and title.
Prop Darren Ryan, wing Andrew Henry and centre Owain Ashman scored tries for the visitors while fly half Chris Anderson landed an early penalty and conversion before the dramatic intervention of Macleod.
Wing Elia Pellegrotti and scrum half Alun Lake replied with tries for the Brewery Field side with fullback Lloyd Warner adding a brace of conversions and penalties.
Llanelli U'21s maintained their pursuit of the runners up position with a 26pts to 21 success away to Ebbw Vale.
Number eight Aled Gravell was in superb form for the young Scarlets scoring two tries, one of which was described as the seasons best. Flanker Steve Thomas was also in fine form while wing Llyr Davies and centre Mark Sweeney crossed for further tries for the visitors.
Fly half Caerlon Thomas secured the victory with a hat trick of conversions. Centre Gareth Roberts and Gareth Green replied with tries for the home side and Ross Watts added a further try and three conversions.
Cardiff v Neath
U21 Cup Final
This Wednesday 24th April, 7.15pm at Bridgend RFC
Wales and Ospreys back row James King, who came through the North Wales age grade system, nominated North Wales Regional Community Rugby Manager Marc Roberts, in the WRU's 'Diolch' initiative where squad players thanked those who played a part in their rise to the top.
Beating Merthyr has boosted Carmarthen Quins hopes of reaching a top eight spot in the Principality Premiership. Quins captain Haydn Pugh is delighted with his team's progress and is determined that everyone from the Under 6s through to the senior team, enjoys the ride.
When the Wales squad were asked to nominate individuals who played a big part in their early playing days, Wales and Dragons full back and wing Hallam Amos thought of his former Monmouth School rugby coach John Bevan.
Sam Cross and Luke Treharne have been named as co-captains of the Wales Sevens side as head coach Gareth Williams names his 12-man squad to play in the first leg of the HSBC World Series in Dubai next weekend.
Bedwas head coach Steve Law and players Nicky Griffiths and Alun Rees extol the virtues of the close knit club as they prepare to host third place RGC 1404 - who are one place head of them on the Principality Premiership points table - on Saturday.
Many of the Wales squad have said Diolch (thank you) to someone who played an important part in their early playing days by nominating them to be invited to the Wales v South Africa match. One person, Gowerton Comprehensive geography teacher Mr Dean Mason was nominated by two of his former pupils, Dan Biggar and Sam Davies.
The second WRU disability rugby pilot has been delivered, this time in Caerphilly schools, culminating in a festival at the Caerphilly Centre of Sporting Excellence, Ystrad Mynach tomorrow. Plans are in place to set up a Disability Rugby Club in Newbridge to provide long-term playing opportunities.
WRU TV: Hear from inside the Wales camp as Neil Jenkins discusses this weekend's clash with South Africa and how the squad are looking to put in a strong performance to round of the 2016 Under Armour Series