Kate wore a stunning red coat, black gloves, boots, and a fascinator-style hat.
She carried a small black bag and wore a subtle brooch of the Welsh Guard's sigil.
The Prince of Wales wore a uniform and gave a speech to the Guards and the public.
Wales is a special place for the royal couple.
William worked as a search and rescue pilot while Kate led a normal life.
They announced a new collaboration to help create therapy allotments and gardens offering mental health support in south Wales.