The young Scarlets lead by 6pts to nil midway through the first half but conceeded the games only try close to half time and with Cardiff fly half Nick Macleod adding the conversion and a penalty it was the Arms Park youngsters who lead by 10pts to 6 at the interval.
Cardiff are virtually assured of the league title ahead of next weekends visit to Bridgend to complete the formalities of the title success and will now play Neath in the cup final. The game will be played at a neutral venue and the date is yet to be decided.
Llanelli started by far the brighter of the two sides but despite their flow of possession failed to convert their advantage into points other than two penalties from fly half Caerlon Thomas, while Cardiff attacked from deep to create their only clear cut scoring opportunity which wing Elgan Jones rounded off wide out.
Fira fly half Macleod converted superbly and his penalty on the stroke of half time gave the home side a lead at the interval.
The visitors responded well after the restart with scrum half Mike Phillips tackled short of the try line after a quickly taken penalty had taken play 50 metres up field and fullback Barry Davies created problems for the home side with a kick upfield before Cardiff regrouped. The home side moved play to within sight of the posts and Macleod calmly added his second penalty of the evening to give his side a crucial 7-point.
Despite the disruption through injury to their front row, the Stradey Park youngsters dominated the set pieces and looked threatening in attack as the crowd of over 500 waited in expectation of a visitors score.
However, Llanelli tried in vain to secure the vital score losing possession at crucial times and despite their endeavour and resolve, the visitors failed to break the final line of defense as Cardiff held onto victory and the chance for their unique double of titles.
Principality Stadium will host the UEFA Champions League Final in six weeks' time. WRU chairman Gareth Davies, Football Association of Wales chief executive Jonathan Ford and Ambassador Ian Rush joined young sports fans at the trophy arrival at the venue to celebrate the magnitude of the event on Saturday 3rd June (kick-off 19.45).
British and Irish Lions captain Sam Warburton is looking forward to bringing together players from Ireland, Scotland, England and Wales for the biggest challenge of their careers - a series against world champions, New Zealand.
For the fifth year running, Wales referee Nigel Owens will be in charge of proceedings at Judgement Day V at Principality Stadium. It promises to be 'extra special' for the Wales' favourite ref, as he will be making his 150th appearance in the league.
There will be no shortage of inside knowledge from Bowl Finalists Caerphilly and Amman United when they face each other on Sunday at National Finals Day. Caerphilly hooker Rhys Cleverly knows the Principality Stadium pitch better than most as a matchday groundsman, while Amman United can look to Wales' record try scorer Shane Williams for some helpful advice.
Two hundred and 40 teams competed in the inaugural Urdd WRU 7s held at Pencoed last week with Welsh internationals Steff Andrews and Jasmine Joyce impressed with the talent on display, as was Urdd chief executive, Sioned Hughes.
The countdown is on for Judgement Day V as tickets for the big day at Principality Stadium soar through the 50,000 mark. Players and coaches alike are bursting at the seams to play in the double header with Dragons coach Kingsley Jones claiming there is a 'real buzz' about the event.
WRU TV went behind the scenes when the four regions got together to test their skill set for the BBC's Scrum V Live rugby show, at the WRU National Centre of Excellene in the build up to Judgement Day V. Blues' Matthew Morgan was one of the stars of the show while the Dragons' Cory Hill proved a surprise package...the full set of results will be revealed on tv screens on matchday
Wales assistant coach Richie Pugh is confident his side can cause a few headaches in the Hong Kong Sevens this weekend. In a tough group, Wales kick off their campaign against New Zealand on Friday before playing Japan and Fiji, who are chasing their third consecutive Hong Kong title, on Saturday.
Bedwas had to overcome a stubborn Carmarthen Quins side before winning the Foster's Challenge Cup final in Bridgend with a 23-18 victory. Bedwas captain Nicky Griffiths pays tribute to his side who have claimed the club's first piece of silverware in the modern era.
Team coach Brett Davey is aiming to keep his unbeaten run in cup finals at Principality Stadium intact when his side take on Amman United in the WRU Bowl final, after he guided Caerphilly to a 20-14 win against Cilfynydd in the semi-finals.
Penallta are hoping to go one step further than last season when falling to Bedlinog in the WRU Plate Final. After a titanic struggle against Nant Conwy, they have given themselves a great chance, after a hard fought 18-13 semi-final victory.