|Judgement Day: Blues v Ospreys; Dragons v Scarlets|
|Venue: Millennium Stadium, Cardiff Date: Saturday, 25 April|
|Kick offs: 14:30 BST and 16:45 BST Coverage: Blues v Ospreys live on Scrum V Live on BBC Two Wales, BBC Radio Wales, BBC Radio Cymru, online, mobile, the BBC Sport app and Connected TV. Dragons v Scarlets live on S4C, BBC Radio Wales, BBC Radio Cymru, online, mobile, the BBC Sport app and Connected TV. Live text commentary on both matches on BBC Sport website.|
Lyn Jones predicts Welsh Rugby's Judgement Day will become a sell-out in future at the Millennium Stadium.
On Saturday Cardiff Blues face Ospreys and Newport Gwent Dragons play Scarlets. It is the third year back-to-back derbies are being staged there.
The event began in the 2012-13 season.
More than 40,000 tickets have been sold for the Pro 12 games at the 74,000-seat venue. Dragons rugby director Jones said: "Within three years this is going to be a capacity event."
He added: "It's like the Welsh Cup was - from 1972 up to about 1986 it was a 20 to 30,000 attendance.
"But it became a sell-out very quickly and the occasion grew and grew once people got the flavour of it.
"And likewise Judgement Day is going to get bigger and bigger and finding tickets in the future is going to be difficult."
The Welsh Cup final used to be the biggest domestic game in Wales until the introduction of regional sides in 2003 took the best players out of the competition.
The introduction of back-to-back derbies between the four Welsh regions at Cardiff's Millennium Stadium was designed to establish a new showpiece event.
The Welsh Rugby Union predicts a 2015 crowd in the region of 50,000, which would be the highest since the event started in 2013.
Fans are also going to vote on whether the Millennium Stadium's roof will be open or shut for the event.
However Jones, who played club rugby for Neath and Llanelli, says one element of the old derby matches is missing.
"I don't think the rivalry has been lost, it's just changed in its format from playing local derbies amongst Neath and Swansea etc," he added.
"It's not about fisticuffs in the first five minutes, which was the tradition.
"It's about playing faster and harder now and you have to have an appreciation for that compared to squaring up to each other."