Queen Elizabeth II’s favorite outfits will be curated in an exhibition titled “Fashioning a Reign: 90 Years of Style from The Queen’s Wardrobe” that will kick off at the Palace of Holyroodhouse in Edinburgh on April 21. Royal fans will get a glimpse of the queen’s wardrobe to mark her 90th birthday.

To be held at the Palace of Holyroodhouse in Scotland, the exhibit will explore tartan outfits and will display the queen’s most-treasured outfits from her childhood to the present day. It will be the biggest ever public collection of her possessions, housing 150 of her favorite outfits.

It will be the first of three exhibitions that will be held in honor of the 89-year-old royal’s milestone birthday. The Royal Collection Trust said on Friday that the outfits in Scotland were chosen to represent “significant events in the queen’s life and reign, Her Majesty’s support of British craft and design and tartan in royal dress.” Several iconic outfits will be displayed in the open, outside of glass cabinets to give people “full, open view.”

Some of the significant events to be shown through the contents of her wardrobe include Elizabeth’s wedding to Prince Philip, her coronation and official state visits.

The confections created by her designers like Sir Norman Hartnell, Sir Hardly Amies and Ian Thomas feature in the exhibition. For instance, there is a turquoise-blue dress with matching bolero designed by Norman Hartnell for her sister Princess Margaret’s wedding in 1960. Making fashion history, it was the last time that members of the royal family wore full-length day dress for a family wedding.

There are also several unique tartan sashes and shawls in the exhibit. Visitors will get a rare glimpse of a cream embroidered duchesse satin Norman Hartnell evening dress with a sash of Royal Stewart tartan that Elizabeth wore to the Gillies Ball at Balmoral Castle in 1971.

The exhibition also features a woven silk-velvet tartan dress worn by Queen Victoria in 1835 as an early example of tartan in the royal family.

The tradition of wearing tartan in Scotland began around 1538 and originated in the Highlands. The design was championed by Queen Victoria, whose husband Prince Albert designed the famous Balmoral tartan in the 1850s, which to this day can only be worn with the Queen's permission.

The second collection will go on display as a part of the annual summer opening of the State Rooms at Buckingham Palace from July 23, while the final exhibit will take place at Windsor Castle from Sept. 17.