The couple announced on Monday that they are to wed after a 16-month romance. More details about Harry's wedding to his American fiancee are set to be released later.
On a visit to a London museum, the Duchess, who is pregnant with her third child, said: "William and I are absolutely thrilled.
"It's such exciting news. It's a really happy time for any couple and we wish them all the best and hope they enjoy this happy moment."
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The Duchess of Cornwall said "America's loss is our gain".
"We are all absolutely delighted," Camilla said, speaking during a visit with the Prince of Wales to Stoke-on-Trent.
"As you can see, they are so happy."
A March or May wedding date is thought to be most likely, given the number of Royal events next year.
April is not considered the best month as that is when the Duchess is expected to give birth and the Queen is occupied with the Commonwealth Heads of Government Meeting.
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The wedding venue for the church service could also be confirmed, with St George's Chapel at Windsor Castle thought suitable.
A smaller venue, it is considered appropriate for the Prince, the fifth-in-line to the throne.
However, the couple may go for a full-scale fairy tale ceremony instead and choose Westminster Abbey, where William and Kate wed, or St Paul's Cathedral, where Harry's parents married.