‘Is it made with Liffey water?’ Philip enquires of Guinness
Philip asked master brewer Fergal Murray whether the famous stout was made using water from the River Liffey.
The Duke was swiftly told the water was piped from the Wicklow Mountains. It is then used in the brewing process to help produce Guinness's characteristic burnt taste at the historic St James' Gate site.
A Guinness spokeswoman said: "It was a throwaway remark made as part of the banter at the bar between Philip and the master brewer."
Today the Liffey was murky-looking and mud flats could be seen on part of it. The Guinness brewery overlooks the river to the west of the city centre and the smell of hops waft on the air. It uses pure water with a low mineral content.
Arthur Guinness set up his first brewery in Leixlip, Co Kildare, in 1756 after he was left an inheritance by his godfather, Archbishop Arthur Price.
He later handed the business to his brother and, in 1759, signed a 9,000-year lease on the St James's Gate Brewery for an annual fee of £45.
Ten million glasses of Guinness are sold around the world every day.
The Queen (85) was also given a "windows tour" of Dublin by RTE’s Ryan Tubridy from the sixth floor of the Gravity Bar. He discovered two years ago that he was related to Edward III, King of England and France in the 15th century.
Later, the Queen met Taoiseach Enda Kenny and senior Cabinet members at Government Buildings in Dublin.
The Union flag flew alongside the tricolour on top of Government Buildings - built in the final years of British rule - as the historic meeting took place.
The royal couple received a round of applause on two occasions from government staff looking on.
During the engagement with the Taoiseach, the royal couple were also greeted by Tanaiste Eamon Gilmore and his wife Carol Hanney.
They paused to admire a stained glass window by Dublin painter and stained glass artist Evie Hone, which was exhibited as part of the Irish pavilion at the 1939 World Trade Fair in New York.
It is entitled My Four Green Fields and represents the four provinces of Ireland, the Three Crowns of Munster, the Red Hand of Ulster, the Harp of Leinster and the half spread eagle and the sword for Connaught.
The royal couple sat by the fireside in the Taoiseach's office for a private talk with the Taoiseach and Fionnuala Kenny before being invited to sign the visitor's book.
The Queen and Duke were then introduced to Ceann Comhairle, Sean Barrett in the Taoiseach's meeting room before moving on to meet coalition ministers and the Attorney General Maire Whelan.
The royal couple were then shown two excerpts from the Waterford Charter roll, with Waterford museum director Eamonn McEneaney detailing the document.
Dating from 1372 and measuring some four metres in length, the parchment roll contains portraits of five medieval kings of England - Henry II, John, Henry III, Edward I and two contemporary portraits of King Edward III.