Kate placed a bouquet of flowers into a sea of other floral tributes, with a poignant note attached.
The note read: 'To Vichai and all those who died in this terrible tragedy, you will be sorely missed. Our sincere condolences to the city of Leicester,' reports The Sun.
It was signed from 'William' and 'Catherine'.
Prince William also spoke with Mr Srivaddhanaprabha’s son, saying he 'knows how devastating it is to lose a parent amid the gaze of the world.'
The Prince told fellow mourners he was 'lucky' to have known the wealthy businessman for several years.
'Catherine and I wanted to visit Leicester to pay tribute to a man that we knew, Vichai Srivaddhanaprabha and those who died alongside him in October,' he said during a speech.