Heather Lind, 34, said the incident occurred four years ago at an event to promote the TV series "Turn: Washington's Spies," according to the Daily Mail, which saved a screenshot of a lengthy Instagram post she wrote and later deleted.
It is the latest in an outpouring of sexual harassment allegations against powerful male figures in entertainment, fashion and finance that followed the downfall of movie mogul Harvey Weinstein, who stands accused of assaulting and raping actresses.
Lind added she decided to share her story after seeing Bush Sr, 93, appear onstage at a benefit concert to raise money for victims of the hurricane-ravaged southern United States and Caribbean.
"I found it disturbing because I recognize the respect ex-presidents are given for having served," she wrote.
"But when I got the chance to meet George H. W. Bush four years ago to promote a historical television show I was working on, he sexually assaulted me while I was posing for a similar photo.
Later on, as pictures were being taken, Bush repeated the act, while "Barbara rolled her eyes as if to say ''not again.'"
In a statement circulated to the Daily Mail and the New York Daily News, a spokesman for Bush did not deny the allegation but said it was an ill-judged attempt at humor.
"President Bush would never -- under any circumstance -- intentionally cause anyone distress, and he most sincerely apologizes if his attempt at humor offended Ms. Lind," the statement said.
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