Merthyr survived a late onslaught to beat Rhiwbina 29-26 and take home the Swalec Plate at the Millennium Stadium.
A brace of tries from Owen Morgan and further scores from Josh Flye, Osian Davies and Gareth Way sealed a league and cup double for the Ironmen.
Rhiwbina got off to a flying start with tries Brett Chatwin and Sion Summers, but were out-muscled by the Division 1 East champions.
Louis Millar and Chatwin scored late tries to pull the Squirrels back to within three, but Merthyr survived a late scare to take home the Plate.
Rhiwbina stormed into the lead after a well-worked try from wing Chatwin. Outside-half Josh Davies executed a pinpoint cross-kick which found Chatwin, and the Squirrels flyer was too quick for the covering Merthyr defence.
The underdogs stretched their lead after 17 minutes with another score out-wide. The Rhiwbina backs spread the ball to the right flank and Chris Fido offloaded back inside for onrushing full-back Summers to crash over - Gareth McCarthy added the extras.
The Ironmen replied just moments later through full-back Fyle.
The Merthyr forwards tried to shove there way over before releasing the backs who pushed the ball to Fyle.
The full-back dummied his way through the scrambling Rhiwbina defence and touched down to pull his side back to within seven points.
Flanker Davies then found a gap in the opposition defence to complete Merthyr's 12 point comeback.
The back-rower darted through a hole in Cardiff side's defence to score from 10 metres out, fly-half Steve Lang added the extra two points to draw his team level on half-time.
Merthyr, who are a division above their Plate rivals, took the lead after 47 minutes.
The pressure finally told when Morgan squeezed in at the corner following Luke Harwood's offload, taking the score to 17-12.
Morgan scored his second soon after, the lightning winger rounded his opposite man and dived over in the same corner.
Way then crashed over for Merthyr's fifth try to seal the win.
Millar and Chatwin scored late tries to take their team to within three points, but they couldn't get over the line for the winning score.
Wales Under 18 captain Callum Bradbury is delighted to have seen his side claim a narrow 18-17 victory against a strong SA Schools 'A' side to end the three-match Under 19 International Series in South Africa on a high note.
The Wales U18 squad spent an emotional day in the drug-riddled townnship of Hout Bay. Hout Bay Warriors President Fred Johannes said the visit was 'the talk of the town' and will dream about the day everyday for the rest of his life.
RGC 1404's new head coach Mark Jones is hoping to build 'something special' in north Wales and is already looking forward to the development region participating in the Principality Premiership for the very first time.
A joint venture between the WRU and Admiral saw hundreds of children enjoy the Admiral Festival of Rugby held at the National Centre of Excellence at the weekend where Welsh internationals Sam Warburton, Scott Williams and Rob Evans were in attendance.
Wll Jones leads Wales U18s into battle this afternoon against Italy where the Welsh side will be seeking to bounce back from their narrow defeat to SA Schools in their opening clash of the U19 International Series
All four regions attended a successful training camp staged last weekend at the WRU National Centre of Excellence. It was a chance for new Wales Women's head coach Rowland Phillips to deliver his key messages to players and coaches as he prepares for the new season.
Wales U18 Team Manager Gethin Watts believes the next couple of weeks will be 'extremely beneficial' to the future of Welsh rugby as his side prepare to take part in the Under 19 International Series being staged in South Africa.
The WRU is searching for 12 new rugby development apprentices following a successful first year of its WRU Coach Core programme. Craig Duncan and Jess Hancock have flourished in the first year of the programme which has given them a real direction in their lives.
The WRU signed TV comedian Rhod Gilbert up to a 'Coaching Children Level 1' course before letting him loose on an U8s side at Whitland Junior Borderers - we went behind the scenes to film the making of 'Rhod Gilbert's Work Experience' see the results here.
Llandovery are aiming to make it three titles in a row in this year's Foster's National 7s being held at BT Sport Cardiff Arms Park on Sunday 28 August. Drovers assistant coach Simon Davies and Lee Rees assess their sides chances
A pioneering strength and conditioning programme has been delivered to more than 8000 boys and girls at hub schools throughout Wales this season, helping to develop stronger, more flexible athletes for rugby and other sports.