Dbodygerry Adams has disclosed that his father was a thug and a paedophile. It is an extraordinary revelation that will now feature in every history written of the IRA.
Gerry wants us to hear him as an individual speaking for a family, but it is inevitable that the character of Gerry Adams senior and his effect on his son will be examined for their historic relevance.
The question is: what formative influence, if any, did abuse and child rape play in the creation of the Provisional IRA?
Not much, if the father was an exceptionally evil and twisted man, for Gerry, however damaged he might have been himself, cannot be blamed for the whole movement.
But this disclosure, coming against the backdrop of revelations about abuse by priests and members of religious orders, prompts us to wonder just how sick the Catholic nationalist culture was.
Gerry Adams lived with a father, who was a brute, and went to school at the Christian Brothers - many of whom also were sadists.
He gives every impression of being a man who survived that, as did thousands of others.
Indeed some of his contemporaries merely laugh at the suggestion that the Brothers left them with emotional scars.
But those who faced beatings and abuse at school and at home hadn't much space within which to be relaxed and happy.
Perhaps that is a clue to why Gerry Adams writes so sentimentally about the women in his family background, for they provided some escape perhaps.
It may also be a clue to why he often speaks of the republican movement as a family.
He speaks as if his father besmirched the republican tradition, but with an understanding that the tradition itself is noble and decent.
But what if the anger that drove the war was an anger that should properly have been directed at fathers?
Gerry Adams senior was one of a generation of republicans in Belfast that included men like Joe Cahill and Billy McKee.
Would it be news to them that Adams senior was taking sexual release on the bodies of his children?
Gerry junior's claim that this has nothing to do with the party is probably a vain hope and a naive one if he really believes it.
The story raises questions about how the IRA conducted itself, in his generation, towards children.
It orphaned many, including the children of Jean McConville. That was not a conscientious attack on children, but much else that the Provos did was.
Thousands of young men were shot in the legs by them. They were made to lie on the ground and a gun was brought to the backs of their legs in a form of abuse that has strong sexual resonances.
Most of those young men were hoodlums and car-thieves and drug-dealers. Many were sons of republicans and their criminality was a revolt against violent parents.
The single greatest expenditure of small arms fire by the Provisionals was, therefore, in a generational war against young men, many of whom were motivated by violence in the home.
Many sex-offenders were shot dead by the IRA. Gerry says blithely that, even in the 1980s, he would have gone to the RUC and reported abuse to them.
That is implausible and can only have traction among those who don't know their history.
Any other republican who had reported Liam Adams to the RUC, who had done what Aine did, would have been shunted down to the border for a quiet word with Freddie Scappaticci and then shot in the head.
And any other paedophile who had raped a child in west Belfast would have been killed by the IRA, not reported to the police.
What we need now is not a political explanation of the IRA campaign, but a psychosexual one.
And the appaling prospect is that it fits within a yet-larger story of abuse and the contempt for children that festered inside the Catholic Church and the religious orders who taught the young Provos and their fathers.
The question over Gerry Adams is whether he would have become a ruthless warlord and devious politician if he had not been nurtured by a paedophile and educated by sexually conflicted men in black.
And Sinn Fein now has to ask itself whether it can afford to have its modern origins examined in these terms.
There are two possible way this could go for Gerry himself.
He is clearly managing intense personal questions about his past with aplomb. Others would break.
He presents himself now as the patriarch of a large and united family, bravely addressing its pain and moving on.
This may all be absorbed by the wider public as a huge credit to him. He would like us to see him as a compassionate and feeling man and he may succeed.
In that event, he will appear much larger than he is now.
But will he still fit in as the party leader?
He has already redefined himself in one stroke.
Just standing in a room with him will feel different now for many who thought they knew him.
The other possibility is that he will get mired in questions about his conduct. Whatever he says, the most likely reason for disclosing his father's abuse when he did was to remove his niece Aine from the centre of the story about abuse in the Adams family.
That can be read as monumental cynicism.
And the war itself, which he remembers as heroic and warranted, will be re-evaluated in the context of the culture of abuse out of which it grew.
Great family man and survivor, or twisted manipulator whose cynicism can now be explained by a background of abuse; these are the possible images of Gerry Adams that will prevail.
And the rest of the party must be feeling like helpless witnesses to his astonishing story.