Labour Party leader Ivana Bacik has said the loss of Britain's Queen Elizabeth II would see a huge cultural change.
She was speaking after Buckingham Palace earlier said the 96-year-old monarch had been placed under medical supervision at Balmoral Castle in Scotland.
Britain's new Prime Minister Liz Truss said the "whole country will be deeply concerned by the news from Buckingham Palace."
Prince Charles and Prince William are travelling to Balmoral to see her - as is Prince Harry.
Ms Bacik told The Hard Shoulder her death would be a big change.
"On a human level first of all, it's very sad to hear of the family gathering, of the - it appears - imminent announcement.
"And on a human level, anyone would want to send sympathies to somebody... who may be on the verge of passing.
"That's very, very sad."
Referring to her State visit to Ireland in 2011, Ms Bacik said: "Already then she was at a very advanced age.
"But really that visit did so much to strengthen Irish-British relations at the time.
"So I suppose there's that sense - and indeed just the time she had been Queen in England has been so long.
"I think when she swore in Liz Truss this week it was her 15th prime minister."
Deputy Bacik added that such an event touches us all.
"For those of us here in Ireland, and I'm a proud republican... but it certainly is a huge cultural change.
"There's no doubt about that, and a momentous date.
"And of course, again, the human sympathy with her family".