Gossage told his wife's best friend the Harry Potter scribe penned the novel under the name of
Robert Galbraith and the woman spilled the secret to a journalist via Twitter last summer.
In addition to the fine, the SRA also issued a written rebuke to Gossage, a partner at Russells Solicitors, for breaching privacy regulations, the BBC said.
Rowling accepted the law firm's apology and was paid undisclosed damages, which she donated to charity.
Notable deaths of 2014 [PHOTOS]