Kate took over from Prince William as colonel as the royal couple spoke to the guards at Mons Barracks in Hampshire.

William addressed them first saying he was "extremely happy to be celebrating St Patrick's Day" but was also "incredibly sad" as his term as colonel came to an end.

In a speech, he said: "It has been one of the great honours of my life to hold that title; I'm proud of everything it stands for - just as I'm immensely proud of every single one of you.

"While at Sandhurst I had a potential officers visit to the Irish Guards, an experience that placed this battalion firmly at the top of my personal wish list."

However, "operational reasons" stopped him from serving his frontline years with the regiment.

Speaking about his wife, William said: "I may be stepping aside, but in Colonel Catherine you have a committed, focused and already incredibly loyal 11th Colonel.

"As you serve together over the years ahead, know that I will continue to watch you, with huge pride in having been one of you."

Kate took over the address announcing her pride in front of the Irish Guards.

She said: "It really is a true honour to be your Colonel. I am here to listen to you, to support you, and to champion you in all you do - this is a responsibility I do not take lightly."

She mentioned her visit to Salisbury Plain where she met with the 1st Batallion in snowy conditions.

"The day was bitterly cold, and while displaying your skills to yet another visitor was probably the last thing any of you wanted to do, all I saw was enthusiasm, pride and incredible dedication."

She added how impressed she was with the guards' "boundless, irreverent, glorious sense of humour" which made them "unique".

Kate had worn an emerald green outfit with matching heels, and presented sprigs of shamrock to the officers and guardsmen as well as to the Irish wolfhound regimental mascot Seamus.

The Irish Guards played tunes including music from Bill Whelan's Riverdance and the parade finished off with the royal salute as the officers marched past.

William and Kate both took drinks of Guinness after the ceremony, mingling with the guards and discussed the upcoming rugby match between England and Ireland.