London, England (CNN) -- Britain's Prince William carried his mother's engagement ring around Kenya in a rucksack for three weeks before he proposed to his girlfriend Kate Middleton, he said Tuesday after their engagement was announced.
The couple seemed happy and relaxed in their interview, teasing each other about his cooking and his romanticism, each drawing laughter from the other.
"She had 10 or 20 pictures of me up on her wall at university," William said.
No, she responded, it was Levi's ads.
It was me in Levi's, William replied without missing a beat.
They met as students at the University of St. Andrews in Scotland in 2002.
The prince said he'd been torn between asking Kate first if she would marry him, or asking her father for permission before her asked her.
Then he realized her father might say no, so he asked her first, he said.
The couple became more serious when talking about William's mother, the late Diana, princess of Wales.
"Obviously, she is not going to be around to share in the fun and excitement of it all," William said.
Giving Middleton his mother's engagement ring "is my way of keeping her close to it all," said the prince, who is second in line to the British throne.
His mother was killed in a car crash in 1997, the year after she and William's father Prince Charles divorced. They had been separated for several years before that.
"I would love to have met her," Middleton said. "She was an inspirational woman."
But William said there was "no pressure" for Middleton to emulate Diana.
"It's about carving your own future," he said. "No one is trying to fill my mother's shoes."
William and Middleton were friends for over a year at university, and were living together with other friends, before they started dating, they said.
The prince called that a "good foundation," saying "being friends with one another is a massive advantage."
He said his attempts to impress her by "cooking these amazing fancy dinners" had failed, and that she had had to hover in the background to help when he burned or otherwise ruined them.
But other qualities attracted her, he joked.
"I'm obviously extremely funny and she loves that," William said.
Middleton did laugh repeatedly during the interview.
She giggled when the prince asserted that "being a real romantic," he proposed well, and when he said that part of the reason they dated so long before the engagement was "to give her a chance to back out if she needed to."
They'll be married in London in the spring or summer of 2011, Prince Charles's office said Tuesday, saying it was too early to give more specifics.