The couple only informed the Queen and the Prince of Wales of their engagement two hours before it was made public.
He asked the permission of Kate's father, Michael Middleton, only after he had proposed.
Prince William informed Prince Harry of the news by saying: "You've got a sister."
Prince William carried his late mother's engagement ring around in a rucksack in Africa for three weeks before proposing to Kate at a conservation park in Kenya.
William proposed next to a remote lake on the slopes of Mount Kenya 12,000 ft above sea level which they reached by helicopter.
6. They stayed at the Lewa Downs nature reserve which is owned by the family of Prince William's close friend Jecca Craig. He went there shortly after his mother's death in 1997 and also spent his gap year there.
The engagement was tempered by the death of Kate's grandfather Peter Middleton, a former airline pilot, last week aged 90.
The first years of their married life will be spent at a farmhouse on the island of Anglesey.
Prince William's star sign is Cancer while Kate's is Capricorn - considered the opposite sign by astrologists.
The couple's nicknames for each other are "Babykins" for Kate and "Big Willie" for William.
Kate prefers to be called Catherine. Her middle name, fittingly, is Elizabeth.
The Prince's middle names are Arthur Philip Louis.
If Kate becomes Queen she will be the first British monarch with a degree. (2:1 History of Art from St Andrews)
She will also be the oldest spinster bride to marry a future king.
She will be the sixth Queen Catherine, after Catherine of Valois, Catherine of Aragon, Kathryn Howard, Katherine Parr and Catherine of Braganza.
The couple's favourite song is "I Like The Way You Move" by the Bodyrockers.
Kate is famed for her sausage and mashed potato suppers.
A horse named Tocatchaprince stormed to victory in the 1pm race at Fakenham two hours after the engagement was announced. His mother is called Queen For A Day.
Prince William claims he tried to impress Kate with his cooking skills at university – although she often had to rescue his attempts.
The couple dressed as Scarlett O'Hara and Rhett Butler for their final May ball at St Andrews University
Prior to dating Prince William, Kate had a relationship with another St Andrews student, Rupert Finch, who is now a lawyer.
Kate was named the prettiest girl at her halls of residence, St Salvador's.
Prince William said he "knew there was something special about her" from the moment they met.
Their first public kiss was on a skiing holiday in Klosters in January 2006.