Prince Harry will join sporting stars at the Rugby World Cup welcome party - staged on the eve of the global tournament.
England are hosting the sporting spectacle and after the opening ceremony on Friday at Twickenham the national team will play Fuji in the event's first match.
Harry and the Duke and Duchess of Cambridge will be in the stands cheering on England head coach Stuart Lancaster's team as they begin their bid to win the Webb Ellis trophy.
The prince is honorary president of England Rugby 2015, the organising committee staging the tournament, and is expected to speak at the welcome party being held tonight at the Foreign and Commonwealth Office in central London.
It will feature guests from the 20 nations taking part and will be hosted by Rugby Football Union (RFU) president Jason Leonard - a member of the England 2003 world cup winning squad.
Speaking in a video message recorded for the England Rugby channel on YouTube recently, Harry said England Rugby's All Schools Programme had reached its target of getting 400 state schools playing rugby by the time of the tournament.
Harry, who is the programme's patron and vice-patron of the RFU, said: ''It's no secret that I love top flight rugby, but I'm also a passionate supporter of how powerful the grassroots game is in helping to improve people's lives - the values it teaches, the enjoyment it brings and the unity it creates.''
He added: ''With the Rugby World Cup just around the corner, this really is a once-in-a-generation opportunity to deliver the greatest legacy for the game.''
Members of the Royal Family will be supporting the six-week World Cup with Harry and the Princess Royal joining the Queen and Duke of Edinburgh at a Buckingham Palace reception in October for the competing nations and some of the tournament organisers.
William will watch a number of matches with the Duchess of Cambridge in his role as vice royal patron of the Welsh Rugby Union, and on Monday the Duke will attend the Welsh team's welcome ceremony at the Guildhall in London.
World Cup fans will be joined by the Princess Royal, patron of the Scottish Rugby Union, and her husband Vice Admiral Sir Timothy Laurence at a number of matches.
Competing Commonwealth countries will receive support from other members of the royal family, including the Duke of Edinburgh, Princess Eugenie, and the Duke and Duchess of Gloucester.