Ed Miliband's first conference speech as Labour leader was in danger of being overshadowed after a bitter rift with brother David spilled into the open.
Despite putting on a public show of loyalty to his younger sibling as he tried to kick-start his stewardship of the party, a barbed remark by the shadow foreign secretary was caught on camera.
The incident came as Mr Miliband disowned large swathes of the previous government's record, condemning the imposition of tuition fees, lax regulation of the City, and Gordon Brown's claim to have ended boom and bust.
But it was his blunt description of the decision to invade Iraq in 2003 as "wrong" that provoked an angry response from his elder brother. Mr Miliband, who was in the hall to watch the keynote address, turned to Labour deputy leader Harriet Harman sitting next to him and said: "You voted for it, why are you clapping?"
Mrs Harman was seen to reply: "I'm clapping because he is the leader. I'm supporting him."
The episode reinforces the growing sense that Mr Miliband's career on the frontbenches is coming to an end. Speculation had been mounting that he would refuse to serve in Ed's team after being narrowly defeated in the leadership election.
The former foreign secretary has refused to confirm he will stand in shadow cabinet elections, and after his own well-received speech to conference on Monday - when he appealed for Labour to unify behind Ed - wife Louise was spotted in floods of tears backstage.
The new leader will have been hoping to put the controversy behind him when he emerged to set out his vision of how to revive Labour. Mr Miliband vowed to oust David Cameron from power at the first opportunity and save Britain from the "miserable" Conservative agenda of austerity and cuts.
He sought to shake off the "Red Ed" tag applied by critics, and insisted he would have "no truck" with irresponsible strikes called by the unions whose votes propelled him to victory. But union leaders warmly welcomed his support for many of their key priorities on protection for agency workers, family-friendly working hours and the living wage. And business groups voiced concern at his attack on excessive pay and support for a banking levy.
Ed Miliband professed ignorance of the comment when he was approached by the BBC at the conference venue later. "I haven't seen that," he said. "All I know is that David has been incredibly gracious both since Saturday and in response to my speech, where he sent me a very nice message." He added: "Different people have different views about that in our party. I am leading this party in a way to win back votes from people."