The monarch, 95, and her grandson, 39, visited AG Barr's factory, where the iconic Irn-Bru drink is manufactured, on Monday.
The Queen's trip to Scotland marks her first since the death of her husband, the Duke of Edinburgh, in April.
She is staying at her official residence, the Palace of Holyroodhouse in Edinburgh during Royal Week, also known as Holyrood Week.
WATCH: Prince William tries Irn-Bru during Scotland visit with the Queen
In Edinburgh, Glasgow and Stirling, Her Majesty will visit businesses, charities and cultural institutions that highlight the pioneering work taking place to further community engagement, education, technology, and efforts to combat climate change.
The Queen was joined by Prince William, known as the Earl of Strathearn in Scotland, for the first day of her visit on 28 June, and will be accompanied by Princess Anne for outings on Wednesday 30 June and Thursday 1 July.
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The Queen and Prince William were given a tour of the Irn-Bru factory and the Duke even sampled some of the drink!
As he quenched his thirst, he told his grandmother: "You can taste the girders in it."
William was asked by commercial director Jonathan Kemp if he had tried Irn Bru while a student at the Scottish University of St Andrews.
"Not St Andrews" he replied, adding during his time in the Army, Irn-Bru was often a part of lunches, and after raising his glass and sipping said "delicious".
William was also intrigued when Colin Reilly, upstream manager, brought over a small jar containing the clear essence of Irn-Bru – with the recipe a secret only known to three people.
After taking a long sniff the Duke said: "I'm trying to guess what's in it but that's quite hard, isn’t it?"
Mr Reilly said: "I'd love to tell you," and William smiled as he replied: "This is a closely guarded secret."
The Queen beamed as she was handed a beautiful bouquet of flowers during her visit.
The monarch looked lovely in a powder blue outfit for her first engagement of her trip - a nod to Scotland's flag, no doubt.
She also accessorised with a string of pearls, matching earrings and the Pearl Trefoil Brooch.
The Queen unveiled a plaque as she officially opened the factory's new process facility.
The Queen and the Duke then attended the Ceremony of the Keys at the Palace of Holyroodhouse.
The ceremony takes place at the start of Royal Week, where the monarch was officially welcomed to Edinburgh by the Lord Provost, who offered Her Majesty the keys of the city.
Her Majesty, who was handed a bouquet of flowers, inspected the Guard of Honour on the forecourt of the Palace of Holyroodhouse.
The Guard of Honour was provided by the Balaklava Company, The Argyll and Sutherland Highlanders, 5th Battalion The Royal Regiment of Scotland.
They were supported by the Pipes and Drums of The Black Watch, 3rd Battalion The Royal Regiment of Scotland, and the Band of The Royal Regiment of Scotland.
This sweet moment between grandmother and grandson was captured by photographers during the ceremony.
Afterwards, the Queen and William met local volunteers and first responders to thank them for their efforts during the pandemic.