Irish Prime Minister Bertie Ahern and DUP leader Dr Ian Paisley have agreed a date for their visit to the Battle of the Boyne site.
Ian Paisley and Bertie Ahern travel to the Boyne site next month
The visit, on 11 May, takes place three days after the return of devolved Government at Stormont.
The Protestant King William defeated Catholic King James at the County Meath battlefield in 1690.
Mr Ahern invited Mr Paisley to the site during a meeting in Dublin earlier this month.
The taoiseach said he was delighted that Mr Paisely had accepted the invitation.
"I look forward to welcoming him and reviewing with him the work that we are planning for this important place in our shared history," he said.
"I believe that this site can become a valuable and welcome expression of the new relationship that we are building on this island, a relationship that is respectful of its past and all its traditions."
Mr Paisley has already said he will present a 300-year-old musket used in the 1690 battle to the site's visitor centre.
The Protestant Orange Order celebrates William's victory every year on 12 July.