Indeed

“At the end of February 1978 he [Roddy Llewellyn] flew to Mustique for a holiday, but was ‘badly run down,’ and went to hospital in Barbados. ‘His faeces were pitch-black,’ records Nigel Dempster, with off-putting omniscience, in his semi-authorized biography.”

From the book Ninety-Nine Glimpses of Princess Margaret by Craig Brown.