She shook hands and said 'hello' to the guests at the lunch-time event held at the Palm Court Hotel.
She was there to discuss her latest book Rival Queens: the Betrayal of Mary Queen of Scots.
Williams relaid the plot of her academic book of jealousy, love, spies, monarchs and executions with relish - and an infectious enthusiasm and easy humour.
Like Professor Joann Fletcher before her, Williams - a university lecturer and broadcaster - has an easy manner and makes what could be a dry and impenetrable subject play like a soap opera.
That comes from their desire to share an undoubtable passion for their respective aspects of history.
Williams has done the hard work of research - archives and endless libraries - although exotic locations from Paris to Antigua have also been enjoyed by Kate in her search for information about her subjects which have also included Lady Hamilton and Napoleon's lover Josephine.
That means all you have to do is sit back and enjoy being educated and entertained.