Gerald Kildare spent most of his childhood being brought up by his great aunt Lady Adelaide FitzGerald (1860–1942), at Johnstown Castle, County Wexford.

A daughter of George Forbes, 7th Earl of Granard, she was the widow of his great uncle Lord Maurice FitzGerald, and it was felt that she would provide a suitable environment for the future duke.

After the war, the future duke farmed his estate at Kilkea Castle, County Kildare, Ireland, but it proved unprofitable.

It was at his Oxfordshire home that, in 1976, the police were called to prevent his father making off with property worth over £100,000, a painting by Joshua Reynolds and a tapestry.

He died in 1994, but the claim is continued by his son Paul FitzGerald, who filed a suit about this with the Department of Constitutional Affairs in 2006.

The results of the tests found that it was "41 times more probable" that Ms. Crawford and Paul FitzGerald were extremely closely related than were from different families.

The proof that Paul FitzGerald is related to the titled family is the first DNA evidence ever produced in the case, and it strongly supports Mrs Fitz-Gerald Caudhill's long-held claim suggesting that her mysterious father was the son of Lady Hermione, the wife of the fifth Duke of Leinster.