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She handed out sprigs of shamrock to members of the 1st Battalion Irish Guards (and their mascot Irish wolfhound Conmeal) in Aldershot, Hampshire, on Saturday.
The visit to the regiment used to be carried out by her husband William's great-grandmother, the Queen Mother, who died ten years ago. That job was then passed on to Princess Anne, and is now likely to be Kate's role.
The 450 soldiers paraded in full ceremonial uniform of scarlet tunics and bearskins before she gave out the shamrock, which is the floral symbol of Ireland.
She also had a private meeting with senior personnel.
The links with the Irish Guards were cemented when Prince William was made an honorary Colonel in the regiment – wearing the ceremonial uniform on his wedding day last April.