The Duchess of Cambridge is frequently photographed at engagements but the public has rarely heard her voice; her first and only TV interview was to mark her engagement to Prince William in 2010.
This interview for ITV will be her first solo TV interview.
Kate, 34, and other members of the royal family have contributed to the "landmark documentary" which has the working title The Queen At Ninety, and will be a celebration of the monarch's life.
Exec producer Nick Kent said: "We've been fortunate to have the participation of so many members of the royal family to mark this historic milestone in the life of The Queen. It's a remarkable story of an extraordinary life which in so many ways reflects the changing face of the nation."
ITV's Jo Clinton-Davis added: "When The Queen was born 90 years ago, there was no hint that her life would go on to be so profoundly significant in our history. As she reaches her 90th birthday, this film aims to offer a fresh insight into our monarch's life and work."
The two-hour film will air on ITV this spring.
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