The 37-year-old royal was sporting a custom Emilia Wickstead dress along with Gianvito Rossi heels.
Kate was left moved after a young boy rapped a poem to her about losing his mother at a young age.
Little Leo revealed that he was angry and alone and 'was always robbing and stealing, Because I didn't care about my feelings, I wasn't able to move on, Because I was still healing.'
The mother-of-three’s last public outing was at the Anzac Day service at Westminster Abbey, where she was joined by brother-in-law Prince Harry.
Kate Middleton Gives a Speech at Opening of the Anna Freud Centre of Excellence in London