Prince William has joked that the morning sickness of his pregnant wife, Kate Middleton, should be renamed "day and all-night sickness".

"I don't know why they call it morning sickness - they should call it all day and all night sickness," said William. The Prince was attending the Winter Whites Gala in aid of the homeless people charity Centrepoint. He also attended a tennis match at the ­Royal Albert Hall to raise money for the charity, his first solo public appearance since the Duchess's pregnancy was made public.

"It's a long old process but she is getting there. She feels like it is going to go on for ever," he told Centrepoint boss Michael O'Higgins, according to the Mirror.

Speaking to young people from Centrepoint, the Duke of Cambridge recalled the night he spent on the streets in 2009 to experience what it feels like to be homeless. He said Centrepoint gave him the "most inspiring moments" of his life.

"Of course, this was just one night.

"I was cold but safe, and I knew I had a home waiting for me. Many others have no such luck. The cold streets are the only reality they know.

"And yet so often their spirit shines through.

"What these unfortunate men, women and young people could achieve given the right opportunities is limitless. I really believe that".

At the event, he presented the Centrepoint Great Britain Youth Inspiration Award to Novak Djokovic for humanitarian work as UNICEF ambassador in his home country of Serbia, where he has raised awareness of early childhood education.

Meanwhile, a friend of Duchess has revealed that the couple were "overjoyed" by the news that they were to become parents.

"Catherine's been steadily putting on weight since April this year and hasn't been drinking...they've been preparing all summer," said Jessica Hay, an old school friend of Catherine, according to a Mirror report.

Looking smart in a black suit, William spent the event chatting with guests, who included sponsors, donors and young people.

Below are images of Prince William at Winter Whites Gala in aid of the homeless charity Centrepoint at the Royal Albert Hall in London.