Wales' highly-anticipated World Cup clash against England on Saturday will have the added spice of a Royal rivalry.

Prince William, vice patron of the Welsh Rugby Union, has urged Warren Gatland's side to beat their English rivals in the Pool A encounter at Twickenham to keep his brother Prince Harry quiet.

"Unfortunately, I will be watching you with my brother, so I will need a Wales win more than ever," the Duke of Cambridge said while presenting the Wales players with their caps during the team's official World Cup welcome at London's Guildhall on Monday.

Gatland, his players and his staff were in fine voice as they sang the Welsh hymn Ar Lan-y-mor, but the Prince remained jovial. "Thank God the Welsh team play rugby better than they sing," he joked.

Wales have endured a difficult start to the World Cup. Both Leigh Halfpenny and Rhys Webb were ruled out of the entire tournament after suffering serious injuries in the final warm-up game against Italy, while head coach Gatland's crisis worsened when Cory Allen was released from the squad with a hamstring injury picked up in their opening 54-9 victory over Uruguay.

However, the Prince has backed Gatland and Co to overcome their troubles and advance from the so-called 'Pool of Death'.

"Whilst we have been dealt a very tough group stage, I firmly believe that, with a simple, determined, match-winning mindset, this team can progress into the knockout stages and beyond. I look forward to having plenty to cheer about throughout the tournament," Prince William added.

"All of your sacrifices, pain and Herculean efforts are about to be rewarded with the chance to make history in Cardiff and London over the next six weeks.

"We now need to look to the rest of the group and particularly this Saturday's match. This will be one of the biggest clashes of the tournament and certainly of the group stages. I wish you all the best of luck and I look forward to supporting you every step of the way. Cymru am byth! [Forever Wales!]"

The loss of Allen might not be the end of Wales' injury crisis; full-back Liam Williams suffered a thigh injury against Uruguay, while Paul James, Samson Lee and Aaron Jarvis also picked up knocks.

However, Wales assistant Shaun Edwards is hopeful the injury situation is not as serious as it sounds - but admits Gatland may have replacements on standby just in case.

"I'm pretty sure Warren has been on the phone and has got someone ready with his bags packed, ready to dash up here," Edwards said.