Lady Alice St Clair-Erskine (born 1989), also known by her stage name Alice St Clair, is an English actress known for playing Kate Middleton in William & Catherine: A Royal Romance and Flora Marshall in The Crimson Field. St Clair was born in 1989, the eldest daughter of Peter St Clair-Erskine, 7th Earl of Rosslyn and Helen Watters.

She was educated at Heathfield St Mary's School and Bedales School. St Clair is also a poet who works under the name of Alan Moon and a voice-over artist whose work includes Air B and B, BBC Radio 4's Homefront and BBC Radio 3's Words and Music. St Clair spent her early years in Los Angeles, where she worked for Akiva Goldsman before moving to New York City and attending the New York Conservatory for Dramatic Arts on an acting scholarship.