Prince Harry said his late mother would have been “very, very proud” that Prince William was getting married.

The 26-year-old said he would be thinking of Princess Diana on the big day on April 29.

Harry is preparing for a gruelling trek in the Arctic with a group of wounded servicemen who are aiming to reach the North Pole.

Speaking about how his mind will turn to his mother, he said: “Myself, my brother and my father, there will be all sorts of people and the rest of the family that will be no doubt be thinking about it.

“And I hope she would be very, very proud that the big day has come upon him. We all thought that it was never going to happen for him. But it has happened, and I think everyone’s going to be very proud of him.” Prince Harry is his brother’s best man, but with less than a month to go, he admitted he has not yet written his speech.

The third in line to the throne said he would be delivering it with two of Prince William’s close friends, but they will have to watch what they say in front of the Queen.

He said: “I’m doing the speech along with a couple of his friends, so I will take the mickey out of him. I will tell a few stories, but I think my grandmother will be there, so I’ll have to be selective.

“The speech will be like any normal best man’s speech. Between the three of us we will make sure people know the good times and the bad times that he’s had since he was a nipper.”

Prince Harry said he was looking forward to welcoming Ms Middleton into the Royal Family, and that she would become the sister he never had.

He said: “A younger brother or younger sister would have been nicer, but to have a big sister is obviously very, very nice.

“I’ve got to know Kate pretty well, but now that she’s becoming part of the family, I’m really looking forward to getting her under my wing – or she’ll be taking me under her wing probably.

“She’s a fantastic girl. She really is. My brother’s very lucky, and she’s very lucky to have my brother. I think the two of them are a perfect match.”

Prince Harry, who last night slept in a tent in temperatures that reached minus 30ºC, said his brother had been under huge pressure, but that he was right to wait to propose to his future bride. “It’s a big deal,” he said. “It’s not just a normal wedding. It’s a really big decision for him to bring Kate into the family. It’s obviously a huge amount of pressure for him, with the public perception and everything like that.”

Prince Harry however remained tight-lipped about his brother’s stag weekend, and laughed off questions about it, saying he was concentrating on the Arctic challenge ahead.