President Michael D Higgins and his wife Sabina will see their twin son John marry his fiancée Eva.
The couple live in Ullard, near Graiguenamanagh, Co Kilkenny.
The couple are believed to be having Registry Office nuptials, with a party planned in nearby Thomastown with speculation mounting that the celebrations may be in the luxury five-star hotel Mount Juliet.
A spokesperson for the family said: "The President and Sabina are delighted for John and Eva."
The President and Mrs Higgins have four children.
Their daughter, Senator Alice Mary Higgins, has followed in her father's political shoes.
The couple also have twin sons John and Michael, and a younger brother Daniel.
The boys have managed to avoid public attention since their parents moved to Aras an Uachtarain in 2011.
Separately, on Saturday night, the President joined several thousand people on the hill of Uisneach in Co Westmeath where he lit the annual Bealtaine fire.
It is thought he may be the first Irish leader since the last High King (presumed to be Ruaidrí Ua Conchobair) lit the fire almost 1,000 years ago.