The new arrival prompted some good-humoured speculation on his name and title.
DUP leader Arlene Foster said: “We are all absolutely delighted that her Royal Highness has safely delivered a baby boy and would like to wish them both our congratulations.”
Asked if she had any suggestions for names, she noted that DUP MLA Carla Lockhart had rushed from the election count on Saturday to give birth to a boy, whom she has named Charlie. “So perhaps that name is already taken,” she joked.
UUP leader Robin Swann MLA tweeted his welcome for the new arrival. “Congratulations to the Duchess of Sussex & Prince Harry on the birth of their baby son,” he said. “PS Robin is a nice name.”
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Lagan Valley MP Sir Jeffrey Donaldson also tweeted his support. “Congratulations to the Duke & Duchess of Sussex on the birth of their son!” he said.
The Orange Order’s Grand Master, Edward Stevenson, said it was “delighted by today’s wonderful and uplifting news”, and on behalf of its membership, he wished to convey “our warmest congratulations to the Baron and Baroness of Kilkeel on the birth of a baby boy”.
“This will be met with great joy, particularly here in Northern Ireland; and will be celebrated across the whole of the UK, the Commonwealth, and indeed the wider world; including among the Orange fraternity in the Republic of Ireland.”
TUV leader Jim Allister said people across NI will be “as delighted as I am to hear news of the new Royal baby”. He added: “Hearty congratulations go to the happy parents and grandparents. While the birth of any child is a happy occasion for a family, the birth of a Royal baby is something which unites the nation in celebration.”
Mid and East Antrim Mayor Lindsay Millar also extended “the warmest of congratulations”. She added: “The new arrival has such special parents to help guide them, and we look forward to welcoming them to Mid and East Antrim in the future.”
Mournes councillor Henry Reilly sent his best wishes to the couple, mindful of the fact that they also hold the titles Baron and Baroness of Kilkeel.
“I am delighted for the happy couple,” he said. “They and their new baby can be assured they will be given a very warm welcome if they visit the home of their title, in the Kingdom of Mourne.” He added: “I like the Duke of Annalong as a title for their new boy.”