The Duke And Duchess Of Cambridge Attend The Annual Irish Guards St Patrick's Day Parade at Cavalry Barracks on March 17, 2018 in Hounslow, England.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge braved chilly conditions to celebrate St Patrick's Day today by attending a parade of the Irish Guards on March 17, 2018

The Duke and Duchess are pictured in Hounslow, west London with the Irish Guards for St Patrick's Day-2018

Prince William enjoys a traditional Irish pint while heavily pregnant Kate sticks to water during their St Patrick's Day celebrations visiting the Colonel of the Irish Guards in Hounslow, west London

Catherine, Duchess of Cambridge attend the annual Irish Guards St Patrick's Day Parade at Cavalry Barracks on March 17, 2018 in Hounslow, England.

The Duchess of Cambridge presents an Irish Guardsman with a traditional shamrock

The Duchess of Cambridge is pictured giggling as she is saluted by a member of the Irish Guard

Prince William, Duke of Cambridge holds an arm around his wife Catherine, Duchess of Cambrdige, who is due to give birth by the end of April, as they watched the parade

Despite harsh winds and chilly temperatures, heavily pregnant Catherine, Duchess of Cambridge smiled throughout the celebrations and chatted to guardsmen.

Kate Middleton grins as she talks to members of the Irish Guards in west London today for St Patrick's Day celebrations

Prince William was left with an unfortunate mark around his head where his hat had been all day

The Duchess of Cambridge presents shamrock to officers and guardsmen of 1st Battalion the Irish Guards as she and the Duke of Cambridge attend the regiment's St Patrick's Day parade at Cavalry Barracks in Hounslow.

The Duchess of Cambridge in a coat by Catherine Walker is pictured stepping out with her husband Prince William, Duke of Cambridge as they arrive for St Patrick's Day celebrations today March 17, 2018

Wolfhound Domhnall - the regiment's longest serving mascot since 1985 - had been doing test runs all week to prepare for his moment in front of the royals

Domhnall's handler, Drummer Aidan Cathcart (pictured right with him), said: 'Domhnall's role is very monumental - he is the first guy on the parade. He is the main guy on the march, it's a pretty important day for him'

Soldiers from the 1st Batallion of Irish Guardsmen line up as they prepare for their Royal visit

The Duchess of Cambridge is pictured stepping out with her husband Prince William, Duke of Cambridge as they arrive for St Patrick's Day celebrations today - March 17, 2018

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, who is due to give birth by the end of April, braved the chilly conditions to attend attend the annual Irish Guards St Patrick's Day Parade at Cavalry Barracks on March 17, 2018 in Hounslow, England.

The Duke and Duchess of Cambridge watched 350 soldiers arrive on the Parade Square before joining in on the festivities

Catherine, Duchess of Cambridge wore a green Catherine Walker coat and a Gina Foster hat as she presented the shamrock to officers and warrant officers

The Duchess of Cambridge smiled and chatted to each of the military men in turn

Heavily pregnant Catherine, Duchess of Cambridge is seen visiting the 1st Battalion at their base in Hounslow, west London

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge braved chilly conditions to celebrate St Patrick's Day today by attending a parade of the Irish Guards

Prince William, Duke of Cambridge in his black Colonel uniform, takes the salute after watching the 350-man regiment march by him, while Catherine, Duchess of Cambridge wears a green Catherine Walker coat and Gina Foster Hat

Catherine, Duchess of Cambridge (R) wearing a green Catherine Walker coat on a visit to Scandinavia and Crown Princess Victoria of Sweden walk through the cobbled streets of Stockholm from the Royal Palace to the Nobel Museum during day one of their Royal visit to Sweden and Norway on January 30, 2018

The Duchess of Cambridge looked incredibly chic in the bottle green coverup by Catherine Walker coat which she teamed with a Gina Foster hat, Kiki McDonough earrings and Troy London faux fur cuffs and scarf.