[1] Iseult's mother Maud Gonne had conceived a child, Georges, with her French Boulangist lover, the prominent anti Dreyfusard journalist and politician Lucien Millevoye.

When the baby died, possibly by meningitis, Gonne was distraught, and buried him in a large memorial chapel built for him with money she had inherited.

Gonne separated from Millevoye after Georges' death, but in late 1893, she arranged to meet him at the mausoleum in Samois-sur-Seine and, next to the coffin, they had sex.

Iseult was educated at a Carmelite convent in Laval, France; when she returned to Ireland she was referred to as Maud's niece or cousin rather than daughter.

With Gonne fearing that Sean's father would seize him from her, her family mostly lived in France until John MacBride's death in the 1916 Easter Rising.

Iseult made headlines during the Second World War when she was brought to trial for harboring Hermann Görtz, a Nazi spy who parachuted into Ireland, a crime to which she confessed but was acquitted.