Washington - Former US President George HW Bush has apologised for jokingly patting "women's rears" after an actress accused him of groping her from his wheelchair while at a screening.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 snr, 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 recognise the respect ex-presidents are given for having served," she wrote.Dirty joke"But when I got the chance to meet George HW 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. "He didn't shake my hand. He touched me from behind from his wheelchair with his wife Barbara Bush by his side. He told me a dirty joke," she added.Later on, as pictures were being taken, Bush repeated the act, while "Barbara rolled her eyes as if to say 'not again'."A Bush spokesperson apologised to Lind for the former president's "attempt at humour"."President Bush has been confined to a wheelchair for roughly five years, so his arm falls on the lower waist of people with whom he takes pictures," a statement from Bush's office read."To try to put people at ease, the president routinely tells the same joke - and on occasion, he has patted women's rears in what he intended to be a good-natured manner."Some have seen it as innocent; others clearly view it as inappropriate. To anyone he has offended, president Bush apologises most sincerely," the statement added.