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 Head Coach Rob Howley talks to WRU TV's Sebastian Barrett about the 36-man squad he has just named for the forthcoming Under Armour series, which includes two uncapped players, Ospreys duo Sam Davies and Rory Thornton.
Head coach Rowland Phillips is deligthed he can now call BT Sport Cardiff Arms Park home for his Wales Women's side, who launch their international season next month with games against Scotland and UK Armed Forces in the heart of the capital city.
Wales Sevens star Sam Cross has put his home town club of Brynmawr on the map after winning a silver medal at the Rio Olympics with Team GB. His club have now honoured him by naming their players bar after him, as WRU TV discovered at the official launch, recently.
One of the newest members of the Principality Premiership, Bargoed admit it's proving to be a steep learning curve at the highest level, but are determined to become a force to be reckoned with. WRU TV visited the club last weekend when they took on Llanelli.
Table-topping Aberavon travel to north Wales to tackle RGC 1404 as both teams defend unbeaten starts to the season in the Principality Premiership. WRU TV's Graeme Gillespie visited the Wizards to see how their preparations were going for the game of the weekend.
The Half a Game initiative is currently sweeping across Wales and proving a major success. The scheme aims to give every young player at least half a game every weekend. WRU TV recently visited a festival in Narberth where clubs have fully embraced the initiative.
Both Bargoed and Swansea were seeking their first win of the Principality Premiership season this afternoon. It proved a fruitful day for the hosts - not only did they win, but Bargoed claimed a try bonus point.
Cardiff managed to keep their unbeaten record at home intact, but only just as Bridgend made them work extremely hard before the Blue and Blacks secured a hard fought Principality Premiership win at the BT Sport Arms Park last night.
Former Wales back row Andy Powell gives a guided tour of The Wern, home of Merthyr RFC, who are determined to prove a lot of people wrong and make their mark in their first season in the Principality Premiership.