Yes, that is a real hat.

arrive to attend the Royal Wedding of Prince William to Catherine Middleton at Westminster Abbey on April 29, 2011 in London, England. The marriage of the second in line to the British throne is to be led by the Archbishop of Canterbury and will be attended by 1900 guests, including foreign Royal family members and heads of state. Thousands of well-wishers from around the world have also flocked to London to witness the spectacle and pageantry of the Royal Wedding.