Stepping out in her stunning Elie Saab wedding dress, Stephanie de Lannoy looked every inch a Princess.
Accompanied by her brother, Count Jehan de Lannoy, the 28-year-old bride walked down to the alter where Prince Guillaume stood waiting.
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Elegant and poised, 28-year-old Stephanie was helped by her bridesmaid and new sister-in-law, Princess Alexandra, who looked pretty in a soft peach dress.
In the morning sunshine the cathederal looked picturesque and crowds of people lined the streets to catch a glimpse of their new hereditary Grand Duchess.
Royal guests from far and wide made the trip to Luxembourg, and began arriving around 10am on the red carpet leading to the grand cathedral's entrance.
The Earl and Countess of Wessex flew the flag for Britain, with Sophie wearing a monochrome Emilia Wickstead dress and a black hat by milliner Jane Taylor.
Danish Prince Frederick was accompanied by his glamorous wife Mary, who sported a stylish grey hat and burgundy peplum dress.
Also gracing the royal red carpet were Prince Haakon and Mette-Marit of Norway, Spanish Prince Felipe and his wife Letizia and the Netherland's Willem-Alexander and Princess Maxima, who dazzled at the previous night's gala dinner.
Xavier Bettel, Mayor of the City of Luxembourg, looked suave as he entered the catherdral for the service which featured more pomp and grandeur that the civil ceremony he conducted on Friday.
Cheers erupted from the crowd as Prince Guillaume, 30, and his mother stepped out of the their car, knowing they were minutes from seeing Stephanie's eagerly anticipated dress.
Europe's newest Princess emerged looking radiant and compossed, sporting a tiara from her own family's collection.
The bride's attendants were dressed in the traditional Nassau colours of blue and orange.
Six-year-old Prince Gabriel, who is the son of Guillaume's brother Louis and his wife Tessy, was chosen to act as a page boy, as was Stephanie's nephew: Lancelot de le Court.
The ceremony, which was conducted in a mixture of French and English, featured a minute's silence out of respect for Stephanie's late mother Countess Alix de Lannoy.
After saying their vows in Luxembourgish, a rousing rendition of Handel's Messiah played as the royal couple signed their marriage certificate.
Visibily more relaxed, Guillaume and Stephanie passed under a traditional saber arch, leaving the cathedral arm-in-arm as they made their way to the Grand Ducal Palace.