Elton John may have been very close to the late Princess Diana, but the singer says he's not counting on getting an invite to her son William's upcoming wedding.

"I think because of my relationship with Princess Diana, people automatically think I'm going to be invited," John told Reuters in an interview.

Prince William is due to marry long-time girlfriend Kate Middleton on April 29 at Westminster Abbey in London.

"I just wish them the happiest of lives together," said John of the couple. "They seem very happy. He's a really terrific man, William, and he's going to be a great king."

John sang a rewritten version of his hit song "Candle in the Wind" at Princess Diana's funeral in 1997 after her death in a Paris car crash.

But he said he did not know her sons William and Harry well. "I'm not invited to the wedding, I would not expect to be invited to the wedding," he said.

"I don't really know the boys at all," John said in a weekend interview. "I met the boys and had lunch with them when their mother was alive. I re-met them again when I did the concert for Diana a couple of years ago -- the memorial concert."

John opened and closed the 2007 London memorial concert, which was organized by William and Harry marking the 10th anniversary of Diana's death.

"They're tremendous boys, but I don't know them (so) it would be presumptuous of me to even talk about them," John said. "They are great boys, their mum would be very proud of them.

"These boys are their own people, they have their own friends, and I just hope that they have the best day and it's sunny and it's a great occasion for them," the singer said.