The heir to the throne is currently in South Africa where he will later host the annual awards ceremony for his multi-million-dollar Earthshot Prize.
He made the trip without Kate who is still recovering from her treatment.
He said she would be cheering him on from their home in the United Kingdom.
"She's doing really well thanks," he told the BBC ahead of his environmental prize's awards ceremony in Cape Town.
"She's been amazing this whole year. I know she will be really keen to see tonight be a success."
As well as Kate, he said he hoped their three children George, 11, Charlotte, nine, and Louis, six, would also be watching on proudly, saying they as a family did what they could to help the environment.
"We go through all the basics of recycling and making sure we minimise water use and turning off lights when we leave the house and stuff like that," he said.
William set up the Earthshot prize to find innovations to combat climate and other green issues in 2020, inspired by US president John F Kennedy's 1960s "moonshot" project which led to the 1969 lunar landing.
Five winners receive a million pounds ($A2 million) every year to drive their projects.
Asked how he could convey his Earthshot message during a tough political climate for environmental causes, he told the BBC: "I think everyone wants some hope and wants some optimism."
He said the young people of Africa who would attend the awards would show how important the issue was to them.
"Without them, you know, the future is looking pretty bleak," he said.
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