In the blink-and-you-miss-it moment, Kate was seen smiling at her husband Prince William as he joked about her having the "easy bit" to say.
WATCH: Prince William and Kate's special St Patrick's Day message
They had joined various world leaders in the heartwarming message for the Irish government. Prince William spoke in Irish Gaelic, saying: "Beannachtaí na Féile Pádraig oraibh", which means, 'Happy St Patrick's Day'.
Kate, who looked beautiful in an apple green boucle jacket and her Daniella Draper shamrock necklace, said: "We're delighted to wish you all a very Happy St Patrick's Day."
Jokingly, William turned to her and quipped: "How come you got that easy bit?" The couple then recalled the warm welcome they received during their visit to Ireland last March just ahead of the first lockdowns.
Royal fans loved this exchange between the couple
"We were so thrilled to be able to visit Ireland just over a year ago, a few short weeks before all of our lives were turned upside down by the pandemic," added William, while Kate continued: "The warm welcome that we received everywhere was a testament to the friendship between our two countries, and the strength of the relationship between the UK and Ireland."
After seeing the sweet footage, fans flocked to social media to comment. "Lovely to see this. These two beautiful royals," remarked one royal fan, while another stated: "I'm so happy to see them genuinely smiling again." A third post read: "Awww gosh, first photo! I really love this video. They are the best couple."
Traditionally, William and Kate would attend the St Patrick's Day parade with the 1st Battalion Irish Guards, where the Duke gives the salute and the Duchess hands out shamrocks to the officers. Last year's public event did not take place as the majority of the regiment were on deployment overseas.
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