A screenshot taken by The Telegraph shows a photograph of a smiling Meghan above a message, dated January 10, which said: “The Duchess of Sussex announced as our new Royal Patron.”
The patronage, which is currently held by the Queen, is likely to suit the duchess, who was an actress before joining the royal family when she married Harry last year.
The couple are expecting their first child in the spring.
A theatre spokeswoman declined to comment, while Kensington Palace would not confirm the patronage.