Denise Evans-Allford and Kevin Allford joined crowds in the Mumbles, Swansea, in the hope of seeing Prince William and Kate on Tuesday.
After giving a note to a security guard, Kate went to meet them giving them a hug.
“In terms of personality she hasn’t changed at all”, they said.
The couple, from Carmarthen, both taught Kate, as well as siblings Pippa and James, at St Andrew’s prep school in Pangbourne, Berkshire in the 1990s.
Prince William and Kate were visiting Joe’s Ice Cream Parlour to talk to parents about the duchess’s UK-wide survey to help improve early childhood.
Mrs Evans-Allford, who taught PE, and her husband, who taught French and German, had not seen the duchess since she was 14, when she visited her brother James at the school.
The pair were waiting in crowds outside the parlour in the hope of seeing the royal couple, when they passed a note on a postcard to a security guard to let Kate know they were there.
They were then taken by security personnel to the front of the crowd and the Duchess came out to see them.
She told them “it’s such a small world”, before hugging them, the couple said.
“She has obviously changed physically since we last saw her, she has grown about a foot but in terms of personality and the way she is, she hasn’t changed at all,” Mr Allford said.
“It was a great occasion for us, it was a very emotional reunion.”
“After she left us, she got in the car next to William and said ‘They’re my former prep school tutors’, and he said ‘Oh, wow’ and made a special effort to wave at us.”
The couple, who lived in a flat at the school at the time Kate studied there, said the duchess and her friends would come around and visit their young daughter Angharad.