CINDY McCain, the glamorous heiress wife of likely Republican nominee John, has broken cover in the presidential race by declaring that she will not make her tax returns public, even if her husband reaches the White House.
Recent US campaign laws, ironically sponsored by her husband, have forced presidential candidates to declare their taxes. The aim was reassure the public that favours are not being bought from wealthy donors.
But Cindy, heir to a reported 150 million brewing fortune, has refused to go public, insisting that her finances are kept separate from her husbands.
"You know, my husband and I have been married 28 years and we have filed separate tax returns for 28 years."
She told the NBC channel's breakfast-time Today show: "This is a privacy issue. My husband is the candidate."
Asked if she would release her tax returns if she became First Lady, she said flatly: "No."
The announcement has plunged the woman nicknamed the "Barbie doll" into controversy, and could threaten to burst her husband's claim to be the "Mr Clean" of American politics.
The McCain family has kept out of the limelight until recently as press attention focuses on the drawn-out Democratic contest between Senators Hillary Clinton and Barack Obama.
But Cindy, 53, has long held a fascination with the American public because her life story makes her a perfect fit as a real-life soap opera diva.
Born with both looks and wealth, she became a high school beauty queen, and married a war hero. She is mother of their four children, including two sons in the military and a daughter adopted from Bangladesh.
But she also tottered on the edge of a life of depression and drugs, with a reported addiction to prescription painkillers. She redeemed herself by leading daring missions to fly aid to the world's disaster zones as a charity figurehead.
Her "Barbie doll" nickname is a reference both to her statuesque good looks and to gossip of much plastic surgery.
Until now she has led a quiet campaign, pointedly insisting that if her husband gets to the White House, she will stay in the background, a contrast to the "co-presidency" envisioned by the Clintons.
But in one lengthy interview this week, she spoke of being "shocked, appalled, and angry" over events in Burma.
She said her husband's campaign would not deploy the "negative stuff" often used against him in the past.
She gained respect from voters in February when standing by her husband after the New York Times hinted that he had had an affair with a Washington lobbyist, a story it later admitted was a ill-advised.
And more than one voter has noticed that John McCain, aged 71, is obviously not short of energy if he can keep an attractive wife 18 years his junior.
But on the tax issue she is on shakier ground.
Campaign finance is the red-hot issue of this election, with the Republicans regularly blasting the Clintons for being slow to declare their tax returns and refusing to say who has donated to the multimillion-dollar William J Clinton presidential library.