Representatives of all 14 nations and tournament organisers attended a reception at Clarence House.
They included Australia captain Cameron Smith and England's star forward Sam Burgess and team manager Barrie-Jon Mather.
"It was quite surreal," said World Cup general manager Sally Bolton. "The Prince wasn't able to get to any of the matches due to his diary commitments but he was keen to do something for the tournament, particularly because of his connections with the Commonwealth.
"He met representatives of all the teams and chatted for a long time to Sam Burgess."
Organisers are hoping the tournament will build on the legacy left by the London 2012 Olympics and say the early signs are encouraging.
A total of 75,370 fans have watched the opening five matches and England will play in front of a capacity crowd of 25,000 for their next match against Ireland in Huddersfield on Saturday.
"Ticket sales have gone mad," Bolton added. "It's going really well. We have been overwhelmed by the interest and demand for tickets.
"We're very pleased with it so far but there is still an awful long way to go.
"We were always confident in what we needed to do to achieve but we needed the players to perform and they have."
- Sports & Recreation
- Sam Burgess