Stephen Jones is out of the Wales side to face England in the Lloyds TSB Six Nations match at Twickenham.
The Llanelli outside half has not recovered from the back spasms he suffered during the week and Iestyn Harris will take his place.
It will be the first time Harris has started a Lloyds TSB Six Nations match in his club position and he will be joined at half-back by his Cardiff partner Rob Howley.
Harris figured at centre in the opening championship match against Ireland and came on as a second half replacement full back against Italy.
Another Cardiff player, Nicky Robinson, has been brought onto the replacements bench to fill Harris' shirt. He was due to play for Wales Under 21 against England Under 21.
England have also had to make a change to their replacements. Sale Sharks outside half Charlie Hodgson has withdrawn through injury and Bath's Iain Balshaw has taken his place.
Nearly 40 players were involved in the first Wales Under 18 training session of the season. WRU National Performance Manager Gethin Watts is excited at the potential shown by the group and expects the Regional Under 18 Championship to hone their skills even further.