Former Taoiseach Bertie Ahern and Tony Blair, the former UK prime minister, have both pulled out of an event in the European Parliament next week marking the 25th anniversary of the Good Friday Agreement.
It is understood that Mr Ahern is attending an event in Boston which clashed with the European Parliament event, and that since he was not going to be present, Mr Blair has also pulled out.
The president of the European Commission Ursula von der Leyen, the European Council president Charles Michel, and the president of the European Parliament Roberta Metsola are all due to speak at a special plenary event marking the anniversary on Wednesday afternoon.
There will also be a cross-party panel discussion involving Irish, American and UK politicians.
The vice-president of Sinn Fein Michelle O'Neill is confirmed as attending as well as Robbie Butler, the Ulster Unionist Party MLA.
The Democrat congressman Brendan Boyle will join the discussion remotely.