The future British king announced his engagement to his long-term girlfriend earlier today (16.11.10) after proposing last month and says he decided to give Kate the band his father Prince Charles gave the late Diana as his way of paying tribute to her.
When asked about the oval blue 18-carat sapphire and diamond ring, William said: 'It was my way of making sure my mother didn't miss out on today.'
Diana - who was divorced from Charles - died in 1997 in a Paris car crash and William and his brother Prince Harry often pay tribute to her.
William and his new fiancee did a photo call at St James' Palace in London, where they showed off the stunning ring and Kate spoke about joining Britain's Royal Family.
She said: 'It's quite a daunting prospect but hopefully I'll take it in my stride. William is a great teacher.'
William's father Charles also spoke of his joy at the engagement and joked it had taken a long time as they had been together for eight years.
He said: 'I'm thrilled, obviously. They've been practising long enough.'
Kate's parents Michael and Carole said they were 'absolutely delighted' and 'thrilled' by the news.
Her father said: 'We have got to know William really well, we all think he is wonderful and we are extremely fond of him.
'They make a lovely couple, are great fun to be with and we've had a lot of laughs together. We wish them every happiness for the future.'