Queen Elizabeth. [File photo]

LONDON -- Buckingham Palace on Monday unveiled a hectic program to celebrate Britain's Queen Elizabeth's 90th birthday this year. Britain's longest reigning monarch will mark her birthday festivities across the country.

The Queen traditionally has two birthday celebrations -- her actual birth date of April 21, and a formal birthday celebration always held in June.

One of the showcase events will be a massive celebration in the private grounds of Windsor Castle (May 12-15).

Tickets for the event sold out within days, but 5,000 complimentary tickets to view the event on large screens in Windsor Great Park are being made available by ballot.

A spokesman for the Queen's birthday celebrations said the Windsor event will be a celebration of the Queen's life, her love of horses, her dedication to the Commonwealth and international affairs and her deep involvement with the Navy, Army and the Air Force.

The spokesman added: "Over 90 minutes, 900 horses and more than 1,500 participants from around the United Kingdom and the world will create a joyful event for the Queen."

"The 90-year journey will take us from the excitement of the birth, through to World War Two, her marriage, the coronation and a reign of more than 60 years," said the spokesman.

"The celebration will use horses, actors, bands and dancers to tell the story. Technology will play an important part in the celebration, with a fusion of the latest video projection, LED effects and theatrical lighting," added the spokesman.

The largest ever exhibition of outfits and costumes worn by the Queen are taking place at three official royal residences to display 150 items from the Queen's wardrobe.

At the Palace of Holyroodhouse in Scotland's capital city of Edinburgh, an exhibition will highlight the use of traditional Scottish tartan in royal dress (April 21 to Oct. 16).

The exhibition at Buckingham Palace (July 23 to Oct. 2) will cover fashions from the 1920s to the 2010s with outfits representing the Queen's childhood, wedding, coronation, royal tours and state visits (August-September).

At Windsor Castle, the fashion exhibition will contrast the Queen's magnificent evening gowns with the fancy dress costumes she wore for wartime family pantomimes (Sept. 17 to Jan. 2017).

The Queen's official birthday weekend in June will be another highlight when the monarch attends a service at London's St Paul's Cathedral on June 10, followed by the traditional "Trooping the Color" ceremony the following day, with a spectacular procession from Buckingham Palace along the Mall to Horseguard's Parade showground off Whitehall.

The climax of the office birthday weekend will be classic British street parties across the country on June 12.

The biggest street party will also be a first for Britain, 10,000 people attending a street party along the Mall -- the long road leading to the palace.

Most of the 150 pounds ($217 dollars) tickets have already been snapped up, but the remainder will be allocated by public ballot in March.

In Edinburgh, two parties fit for a queen will take place on the now-retired Royal Yacht Britannia, used for many years by the Queen on her world tours as a floating palace.