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.
We caught up with Shona and Ellie from the Wales women team ahead of the start of the Women's Rugby World Cup in Paris next month at a recent women's training session to encourage and promote more women and girls to try their hand at rugby. #tryourgame
We hear from the Wales camps in South Africa and New Zealand, as well as the EGM, in this week's principality Welsh Rugby Union Podcast. Defence coach Shaun Edwards and forwards coach Robin McBryde look ahead to the Springboks, Angus O'Brien and Mark Taylor look back at heartbreak for Wales Under 20s, while group chief executive Roger Lewis and chairman David Pickering face the Welsh press after being vindicated at the EGM.
Cross Keys flanker Scott Matthews capped off a fine season when he won the last Principality Premiership Player of the Month award before a surprise visit by Alun-Wyn Jones saw him crowned Best Newcomer of the Year.
Pontypridd's dominance in this year's Principality Premiership was reflected in last night's Awards evening held at the Millennium Stadium where Paul John, Geraint Walsh claimed individual awards while Ponty picked up the Fair Play award as well.
WRU TV's Liz Jones has to contend with an enthusiastic PA as she interviews victorious Pontypridd coach Paul John after he guided his side to victory in the Principality Premiership final at Sardis Road.
Cross Keys head to Sardis Road on Sunday showing no fear as they face Pontypridd in the Principality Premiership Play-off Final. WRU TV's Graeme Gillespie gets the low-down from both camps before the big game.
Defending Principality Premiership champions Pontypridd are chasing an unprecedented double double this Sunday at Sardis Road when they host Cross Keys who are gunning for revenge after being brushed aside in the SWALEC Cup final.
500 days to go to Rugby World Cup and SWALEC Finals Day on the Principality Welsh Rugby Union Podcast. WRU chairman David Pickering and First Minister Carwyn Jones look ahead to the Rugby World Cup, while we hear from all three winners on SWALEC Finals Day, Pontypridd's Dafydd Lockyer, Merthyr's Lee Jarvis and Clwb Rygbi Caerdydd's Gareth Williams, as well as former Wales wing Simon Hill on coaching his village team Llantwit Major.
Carmarthen Quins or Cross Keys are just 80 minutes away from taking on Pontypridd in the Principality Premiership final - but first they have to win Sunday's semi-final play-off at Carmarthen Park (KO 5.30pm).
Hear from all six clubs at SWALEC Finals Day on the Principality Welsh Rugby Union Podcast. We hear from Pontypridd's Dafydd Lockyer, while former coach Dale McIntosh reflects on their British and Irish Cup campaign. Cross Keys backs coach Morgan Stoddart and Wales U20 outside half Angus O'Brien on their challenge. Merthyr's Lee Jarvis and Rhiwbina's Gareth Lintern look at their Plate Final. Clwb Rygby Caerdydd's Owain Tudur and Llantwit Major's Shaun Shea on the Bowl Final. Former Llantwit Youth player Dafydd Hewitt of the Blues also looks forward to the game.
It's crunch time at both ends of the Principality Premiership where Cross Keys and Carmarthen Quins are chasing a home tie in the play-offs while Aberavon and Swansea are attempting to avoid the drop. WRU TV's Graeme Gillespie and Will Thomas preview the action.
Porthcawl recently received a WRU facilities grant and funding from Natwest RugbyForce in order to give their changing rooms a facelift. This came after receiving £10,000 in a WRU facilities grant last year to tarmac their car park. The improvements have already helped to make the club more accessible, not only for their own members and players but for the whole community.
The largest and most comprehensive Principality Premiership coaching conference to date took place on Saturday with members of Wales' national management team passing on their knowledge and best practices to coaches from across the Premiership.