Cardiff beat Bridgend 23-16 at Sardis Road, Pontypridd, to advance to the final of the Konica Minolta Cup. They will meet Llandovery at the Millennium Stadium on 28 April.
The Drovers reached their first final with a shock 20-19 win over local rivals Llanelli at the Talbot Athletic Ground, Aberavon on Saturday.
"We have the potential for a record Premiership crowd in the final, with an east v west clash in Cardiff," said Welsh Rugby Union boss Roger Lewis.