The world's most famous engaged couple turned up in Trearddur Bay, Wales on Thursday -- bearing champagne!

On Kate Middleton and Prince William's agenda in their first joint appearance since announcing their engagement last year: To launch and dedicate a lifeboat!

As 2,000 locals looked on dockside, a smiling Middleton, 29, looked comfortable and super-chic: wearing a feathery hat by Vivien Sheriff and a £520 Katherine Hooker coat.

She and Prince William, 28, sang both the Welsh and English national anthems -- and Middleton knew both by heart! "She looked beautiful while she was singing," an eyewitness tells

Explains a palace spokesperson to Us: "This is their first official engagement as a couple and also the first engagement where Miss Middleton has been invited as a guest of honor." See more photos of William and Kate at the lifeboat event.

(Set to wed on April 29, the couple live in Wales, where Prince William is a search-and-rescue helicopter pilot for the Royal Air Force Base.)

"They both wanted their first joint engagement to take place in Anglesey, a place of much meaning," the palace rep added.

After brief remarks from her Prince, royal-to-be Middleton poured champagne over the "Hereford Endeavor."

The duo -- stealing smiles and glances at one another throughout -- then greeted locals and dignitaries. "They are a lovely couple. He is a great lad and she is a beautiful girl," townswoman Jean Critchley told the Associated Press.

On Friday, the couple will go to their alma mater, the University of St. Andrews in Scotland -- where they first met and fell in love.