The production company responsible for making the Netflix series, The Crown, have arrived in Caernarfon.
Filming for the new series is expected to begin at Caernarfon Castle later in the week. It's thought they will be recreating the investiture of the Prince of Wales which took place at the castle in 1969.
The historical drama, based on the reign of Queen Elizabeth II, will see scenes shot in and around the town.
The production company, Left Bank Pictures, sent out a filming notification letter to local residents informing them that disruption to roads around the castle will begin from November 12.
During the preparation period, the producers warned there may be extra vehicle activity along Castle Ditch as equipment is loaded into the castle.
The time-limited parking bays opposite the castle entrance and Old Courthouse have also been suspended and traffic management will be in place to assist with the loading process.
It's anticipated it will take until Thursday to prepare the castle and that day, work will also begin to prepare High Street and Palace Street, with props teams dressing the streets with bunting and flags, with the assistance of the council's lighting team.
A number of characters have been re-cast for the third and fourth seasons with Peep Show and Broadchurch actress Olivia Colman playing an older Elizabeth II while Tobias Menzies playing Prince Phillip.
Hollywood actress Helena Bonham Carter has been cast as the Queen's sister Princess Margaret.
Although full details have not yet been released, the third series is expected to cover the period from 1964 until 1976 - the time frame for Harold Wilson's tenure as British Prime Minister.
The Aberfan disaster that killed 116 children and 28 adults in 1966 is expected to feature in one of the episodes of the new series.