National Day falls on Tuesday, but celebrations traditionally begin the evening before, with events taking place across the country to mark the Grand Duke's official birthday.
The programme begins at 4pm on Monday with the changing of the guard outside the Grand Ducal Palace on Place du Marché-aux-Herbes.
The Grand Ducal couple are then expected in Differdange at 5pm. Traditionally, the head of state visits a different municipality on the eve of National Day.
Last year, Grand Duke Henri and Grand Duchess Maria Teresa travelled to Esch-sur-Alzette, while the then Hereditary Grand Ducal couple visited Mondercange.
This year, Guillaume and Stéphanie will take part in the National Day eve celebrations for the first time as Grand Duke and Grand Duchess, visiting the country's third-largest city.
Representatives of the municipality, Parliament, and the government will welcome them at Gerlach Park. The programme will include a parade by local associations and an opportunity to meet residents.
Part of the celebrations had originally been due to take place on Place du Marché, while a visit to the 1535° Creative Hub had also been planned. However, the programme has been adjusted because of the high temperatures, and the entire visit will now take place in Gerlach Park.
The official visit is expected to end at around 7pm, but the festivities in Differdange will continue. An open-air Te Deum will begin in Gerlach Park at 7.30pm, followed by celebrations lasting late into the night.
Guillaume and Stéphanie will meanwhile continue to Luxembourg City, where the traditional torchlight procession is scheduled to begin at 9.30pm.
Around 2,800 participants will make their way from Place du Théâtre to Place Clairefontaine. The Grand Ducal couple will watch the procession from the official grandstand on Place Guillaume II.
Fireworks will then be launched from Pont Adolphe at 11pm and are expected to last around 15 minutes.
Concerts will take place throughout the capital during the evening and into the night, with tens of thousands of visitors expected.
The Grand Ducal couple will have little time to rest before the official National Day programme resumes on Tuesday. A civil ceremony will begin at the Philharmonie at 10am, followed by the military parade on Avenue de la Liberté.
The official celebrations will conclude with a Te Deum at Notre-Dame Cathedral at 4.30pm.
