The Queen's Holyrood Week has started with a trip to Cumbernauld. There, Her Majesty and Prince William visited the AG Barr's factory, officially opened a new process facility and unveiled a plaque marking their passage.

       During the visit, the Queen and Prince William, who is known as the Earl of Strathearn while in Scotland, were given an overview of the history of the company.

       It was established more than 140 years ago and has since kept expanding its portfolio of drinks.

       In 1901, it launched IRN-BRU, a carbonated soft drink containing 32 flavours.

       At the factory, the Queen and Prince William also met employees to better understand how the company fits in the local community.

       The Earl of Strathearn was treated to a glass of IRN-BRU while the Queen looked on.

       After tasting the beverage, he told his grandmother: "It’s made from girders!"

       He went on explaining that, while he was in the Army, his Scottish colleagues used to drink it for breakfast.

       Before leaving, the pair signed the visitor's book.

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       Both the Queen and Prince William appeared in high spirits on their first of a long list of engagements in Scotland.

       Her Majesty traditionally spends a few days - normally between the end of June and beginning of July - north of the border, in what is known as Holyrood Week in Scotland and Royal Week in the rest of the country.

       During the week, she stays at her official residence in Scotland, the Palace of Holyrood, in Edinburgh.

       Over the next few days, the monarch will undertake a "range of engagements celebrating Scottish community, innovation and history", Buckingham Palace said.

       While in Scotland, the 95-year-old monarch is set to speak to business owners, charity leaders and staff at cultural institutions that highlight the pioneering work taking place to further community engagement, education and technology in these cities.

       She will also hear more about Scotland's efforts to combat climate change.

       The tireless Queen will reportedly carry out two engagements a day this week.

       While today she is in the company of her grandson, she will be joined on Wednesday by Princess Anne, the patron of several organisations and charities in Scotland.

       The string of engagements will end on July 1, when Her Majesty is expected to travel back to Windsor Castle.

       On that same day, Prince William and Prince Harry will publicly meet at Kensington Palace to celebrate the life and legacy of their mother Princess Diana by unveiling a statue dedicated to her.

       Prince William and the Queen last carried out an engagement together in October, when they visited Porton Down.

       The collaboration of grandmother and grandson appears to have pleased some royal fans on Twitter, with one saying: "Absolutely love seeing them together."

       "Hope to see the Queen and the Duke of Cambridge do many more engagements in the future."

       Another wrote: "How great to see them together again."