The Duke and Duchess of Cambridge, along with Prince Harry, attended a Service of Hope at Westminster Abbey on Wednesday.
The multi-faith service was held to honour the victims of the London terror attack on March 22.
The service was attended by more than 400 faith leaders, firefighters, medics and police officers as well as two hundred diplomatic representatives from across the globe.
Prince William laid a royal wreath during the service which included a card which read: "In memory of the innocent lives; lost to us all on the 22nd March 2017."
The wreath also included another message for the policeman who died in the attack.
“For PC Keith Palmer, and all those who have served our community so valiantly. Your legacy is our way of life. William.”
Afterwards the royals met with the victims families in private.
Kate wore a gray and white Missoni coat and black fascinator for the somber occasion, the same one she donned for the Somme Vigil in France in 2016.