Kate Middleton's cancer video had secret help from sister

Kate Middleton reportedly turned to her sister Pippa Middleton while preparing one of the most emotional speeches of her royal life.

The new biography, William and Catherine: The Monarchy's New Era: The Inside Story, written by author Russell Myers, revealed that Kate leaned heavily on her family during her cancer treatment.

Insiders revealed that Pippa collaborated on the script of the deeply personal video in order to ensure the message felt authentic, reassuring and emotionally grounded.

Myers revealed, "Catherine’s family rallied round with her sister Pippa helping to write the script for the short video statement."

He went on to add that Kate's speech "much like the announcement of the death of Elizabeth II … felt like an earthquake whose reverberations were felt around the world."

Friends say that Pippa Middleton remained constant presence throughout Kate Middleton's recovery, accompanying her to major public engagements and offering private support.

Furthermore, an insider told The Times, "The three siblings are incredibly tight…"

"Pippa not only as a sister, but as a best friend she can confide in. They are extremely loyal to one another," they added.