First, the main line of Carew is descended from William Fitz Gerald, eldest son of Gerald Fitz Walter and Nest, daughter of Rhys ap Tewdwr Mawr, King of Deheubarth. Her dowry was Carew in South Pembrook where the ruins of Carew Castle still stand. Tradition has it that William Fitz Odo Fitz William Fitz Gerald was the first to take the name Carew, i.e, William de Carew.
Second, David Fitz Gerald, bishop of St. David's, was a younger brother of the above William Fitz Gerald. He died 23 May 1176. He had many daughters and a son and heir, Miles Fitz David of St. David's, who accompanied his maternal half-uncle, Robert Fitz Stephen, to Ireland in 1169 in the expedition to aid Dermot, King of Leinster, in the recovery of his throne. He inherited the Barony of Iverk, in Ossory, from his maternal half-uncle Meiler Fitz Henry (died 1220). His decendents were Fitz Davids.
Third, my ancestor Robert Gordon Carew had a sister, Francis ("Fanny") Elizabeth Carew, born in 1853 in Ontario, Canada, who married a Mr. Popocock, and died in 1935 in Fairview, North Carolina. If this is your ancestor, I have more information for you.