William is second in line to the British throne after his father, Prince Charles. He and Middleton's first child would move ahead of his younger brother, Prince Harry, to become third in line to the throne.

Prime Minister David Cameron says he's delighted by what he calls "incredibly exciting" news.

David Cameron, UK Prime Minister, said, "Well good morning. This is incredibly exciting news. I'm sure that the whole country will want to pass their very best wishes to the happy couple, and wish them an incredibly long and happy life together."

Many in the UK are welcoming the royal engagement as a rare piece of good news in an age of economic uncertainty and cutbacks -- a time much like 1981, when millions watched Charles and Diana's fairy-tale wedding.

Christine, London Resident, said, "No! I didn't know! Fantastic! No! That's great! No! I didn't know they'd got engaged! Wow! It's all happening! No! That's great! Let's hope they're more successful than the rest of the family (laughs)!"

Middleton, now 28, is the daughter of a self-made millionaire. Her father worked for an airline, and her mother was a flight attendant, before they started a mail-order business specializing in children's parties.

She met Prince William at the University of St. Andrews in Scotland. They're believed to have been dating since 2003.