Katie Holmes has shared a heartbreaking post via Instagram, detailing her heartbreak at the loss of American writer Joan Didion.MORE: Katie Holmes turns heads in dreamy figure-flattering dressTaking to Instagram Stories, the Dawson's Creek actress posted a moving and emotional tribute to the US literary icon, who passed away aged 87 after a battle with Parkinson's Disease.Katie makes funny faux pas during interviewDidion's publisher Penguin Random House announced the author's death on Thursday.