Britain's Kate, Duchess of Cambridge arrives as patron for The Portrait Gala 2014 at the National Portrait Gallery in central London, Tuesday Feb. 11, 2014. (AP Photo/Olivia Harris, Pool)
Kate Duchess of Cambridge waits to make a few remarks at a fund raising gala at the National Portrait Gallery in London, Tuesday, Feb. 11, 2014. . The Duchess is wearing a dress by British designer Jenny Packham and a necklace on loan from Queen Elizabeth II that was given to the Queen as a gift for her wedding in 1947. (AP Photo/Alastair Grant, Pool)
Kate Duchess of Cambridge talks to guests at a fund raising gala at the National Portrait Gallery in London, Tuesday, Feb. 11, 2014. . The Duchess is wearing a dress by British designer Jenny Packham and a necklace on loan from Queen Elizabeth II that was given to the Queen as a gift for her wedding in 1947. (AP Photo/Alastair Grant, Pool)
This handout photo provided by the National Portrait Gallery, taken in 1960, shows Muddy Waters, by Charles H. Stewart. Curators at the National Portrait Gallery want to know what it means to be cool. They have been studying the uniquely American concept of “cool” and how it became a global export, and the museum now is bringing together 100 photographs of people who helped create the idea of “cool” as a name for rebellion, self-expression, charisma, edge and mystery. It includes musicians, actors, singers, athletes, comedians, activists and writers as photographed by Richard Avedon, Annie Leibovitz and others. (AP Photo/Charles H. Stewart, National Portrait Gallery)
This handout photo provided by the National Portrait Gallery, taken in 1956, shows Frank Sinatra, by Herman Leonard. Curators at the National Portrait Gallery want to know what it means to be cool. They have been studying the uniquely American concept of “cool” and how it became a global export, and the museum now is bringing together 100 photographs of people who helped create the idea of “cool” as a name for rebellion, self-expression, charisma, edge and mystery. It includes musicians, actors, singers, athletes, comedians, activists and writers as photographed by Richard Avedon, Annie Leibovitz and others. (AP Photo/Herman Leonard, National Portrait Gallery)
This handout photo provided by the National Portrait Gallery, taken in 1950, shows Marlon Brando. Curators at the National Portrait Gallery want to know what it means to be cool. They have been studying the uniquely American concept of “cool” and how it became a global export, and the museum now is bringing together 100 photographs of people who helped create the idea of “cool” as a name for rebellion, self-expression, charisma, edge and mystery. It includes musicians, actors, singers, athletes, comedians, activists and writers as photographed by Richard Avedon, Annie Leibovitz and others. (AP Photo/National Portrait Gallery )
This handout photo provided by the National Portrait Gallery, taken in 1951, shows Billie Holiday, by Bob Willoughby. Curators at the National Portrait Gallery want to know what it means to be cool. They have been studying the uniquely American concept of “cool” and how it became a global export, and the museum now is bringing together 100 photographs of people who helped create the idea of “cool” as a name for rebellion, self-expression, charisma, edge and mystery. It includes musicians, actors, singers, athletes, comedians, activists and writers as photographed by Richard Avedon, Annie Leibovitz and others. (AP Photo/Bob Willoughby, National Portrait Gallery)