Kate married Prince William in London in April. Her equally fashionable sister became a surprise celebrity after serving as her attendant at the high-profile ceremony.
E! said it will air "True Hollywood Story: Kate and Pippa" Wednesday.
"Kate walked into Westminster Abbey a commoner and emerged a royal duchess," E! said in a news release Friday. "Ironically, on the day of the wedding, Kate wasn't the only commoner to attract international attention. Her younger sister, Pippa, became an overnight sensation, clad in an ivory gown that highlighted her enviable figure. 'E! True Hollywood Story' paints a portrait of these dynamic siblings who have captured the affection of millions around the globe. From their quaint childhood, through their times on the London social scene and finally to where they are today, 'THS' reveals the remarkable story of two beauties who rose to celebrity status in the most magical way."