"The Silkworm", to be published on June 19, will be a follow-up to "The Cuckoo's Calling", which Rowling wrote using the Galbraith pseudonym.
"Robert Galbraith's second Cormoran Strike Novel THE SILKWORM to be published 19/06/14," the author's alter ego said in only a third-ever tweet, with a link to Galbraith's website.
The new novel follows private detective Cormoran Strike in another adventure with his assistant Robin Ellacott.
This time they try to unravel the death of writer Owen Quine after first being called in to probe his disappearance.
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The first book, which saw Strike investigate a model's suicide, was published in April 2013, to critical acclaim. Two television companies had expressed an interest in adapting the novel.
Sales were low, but when Rowling was outed by a newspaper in July, they rose an astonishing 41,000 per cent in a week.
The lawyer who blew Rowling's cover was fined USD 1,670 for breaching the privacy rules of his profession.
Gossage was also issued with a written rebuke from the Solicitors Regulation Authority.
Galbraith was originally described by the publisher as a former member of the Royal Military Police who had been working in the civilian security industry for the last decade.
This backstory provided him with "a solid excuse not to appear in public or provide a photograph", Rowling said.
Rowling, 48, said she wrote under a pseudonym because, as one of the world's most famous authors, she had been yearning to "work without hype or expectation and to receive totally unvarnished feedback".