Known for her thrifty ways when it comes to her wardorbe, fashion fans were not surprised to learn that the Duchess of Cambridge's pine green coat was a sale item from Hobbs.
Originally £279, the Persephone trench has been reduced to £195 and is still available in all sizes on the retailer's website.
She paid further tribute to the Irish feast day with a gold shamrock brooch that belonged to Queen Alexandra and wore a green hat from Gina Forester. Green Amethyst and diamond drop earrings from Kiki McDonough completed the look. Prince William was resplendent in military uniform, attending as Colonel of the regiment.
It is Kate's third consecutive year at the event. The previous two years, Kate wore the same Emilia Wickstead green coat.
Excitement was in the air as some 300 men from the 1st Battalion Irish Guards waited for William and Kate to make their entrance. As they arrived, the national anthem was played.
The Duchess, 32, was tasked with presenting the traditional springs of shamrock to officers and guardsmen. The shamrocks were then passed on along the ranks — a custom that was started in 1901 by Queen Alexandra.
One special recipient to receive a sprig from Kate was Domhnall, the Irish Guards' official mascot. The Irish wolfhound, who has the rank of Guardsman and can apparently be promoted for good conduct, had been especially groomed for the royals' visit.