A "diary secretary" refers to a person who manages someone else's schedule and keeps track of their appointments, tasks, and important dates in a diary or calendar. Full definition
I am often in envy of my colleagues who sit in their plush Portcullis House offices in Westminster while I sit in my draughty cold office alongside the ghosts of past diary secretaries. (totalpolitics.com)
Ever the dutiful diary secretary, I flagged up the fact that she'd need to leave London in the afternoon, travel up and back to the capital, expecting her to ask me to send her apologies. (totalpolitics.com)
Susan Jane Nye, Baroness Nye (born 17 May 1955)[1] is the former Director of Government Relations and former diary secretary to ex-British Prime Minister Gordon Brown. (en.wikipedia.org)