Prince William is to become Baron Carrickfergus - reviving a title which became extinct in 1883.
An Irish Viscountcy of Chichester of Carrickfergus, now held by the Marquess of Donegall, was created in 1625, but Carrickfergus alone existed as a title between 1841 and 1883.
The 3rd Marquess of Donegall was created Baron Ennishowen and Carrickfergus, of Ennishowen, Co Donegal and Carrickfergus, Co Antrim.
He died in 1883, being succeeded by his brother, and the barony became extinct.
Carrickfergus is County Antrim's oldest town.
The word means Rock of Fergus and as an urban settlement it predates Belfast.
It is on the north shore of Belfast Lough, and the site of Carrickfergus Castle which dates from about 1180 and is one of the best preserved castles in Ireland.
The town gives its name to one of Ireland's most beautiful and haunting folk songs, a lament from one of its many sons who emigrated abroad.
It has a beautiful coastline setting along the Lough with views to Scotland, and is home to a wide range of wildlife, including seals, eagles and guillemots.
The castle overshadows an ancient harbour and the town centre boasts modern shops and restaurants, enclosed within 16th century stone walls, to attract large numbers of tourists.