Beyoncé Knowles and Jay-Z have denied they are to marry this weekend.The couple are holding a four-day celebration on a yacht off the Caribbean island of St. Barts to mark the rapper's 37th birthday, but have denied rumors that it is actually a secret wedding ceremony. A spokesman for Beyoncé said: "These reports are not true."And a representative for Jay-Z said: "I have no knowledge of this."Rumors of a wedding surfaced after the pair - who have been dating for around four years - were over heard excitedly taking about a special four-day celebration. A source said: "Beyoncé is throwing Jay a four-day birthday party, but it's really a wedding."Insiders say friends and family invited to the celebrations were told to have passport applications ready by last Friday so they could witness the pair exchanging vows. The four-day event will begin on a luxury yacht before guests are ferried to the paradise island of Anguilla for the wedding ceremony, which will take place at the five-star resort of Cap Juluca. Beyoncé and Jay-Z reportedly visited the exclusive venue earlier this year and decided it would be perfect for their big day.