Kate Middleton underwent a medical exam before marrying Prince William.

The exam was conducted to ensure a future queen could have children.

The revelation was brought to light by royal commentator Daniela Elser.

Kate's fertility was a critical factor in her being cleared to marry Prince William.

The marriage could have been called off if she had failed the exam.

The same exam was conducted for Princess Diana before her marriage to Prince Charles.

Kate's womb is considered the reason she is on the fast track to becoming a queen.

These insights were published on news.com.au.

Author Tom Quinn made a similar revelation in his book Gilded Youth.