LONDON – The mystery has been solved.

A British law firm admitted Thursday that one of its partners inadvertently revealed that J.K. Rowling was the author of a mystery novel, “The Cuckoo’s Calling.”

The Sunday Times newspaper revealed over the weekend that the “Harry Potter” author had penned the book under the pseudonym Robert Galbraith.

The newspaper said it had received a tip on Twitter, and there was speculation that Rowling or her publisher were behind the revelation, which has sent sales of the thriller skyrocketing.

But the law firm Russells said Thursday that one of its partners, Chris Gossage, had let the information slip to his wife’s best friend, Judith Callegari — the woman behind the tweet. Her Twitter account has now been deleted.

A phone message left for Callegari was not immediately returned.

Russells said in a written statement that “we apologize unreservedly” to Rowling. It said that although Gossage was culpable, “the disclosure was made in confidence to someone he trusted implicitly.”

Russells, a specialist in entertainment law, said it informed Rowling and her agent once it learned what had happened.

“We can confirm that this leak was not part of any marketing plan and that neither J.K. Rowling, her agent nor publishers were in any way involved,” the statement said.

“The Cuckoo’s Calling” had garnered good reviews but had sold in the hundreds of copies since April, ostensibly as the first novel of a former soldier. Since Rowling was outed as the author, it has topped best-seller lists, with publisher Little, Brown and Company commissioning a new printing of 300,000 copies.

Marc Anthony to critics: I’m a New Yorker

NEW YORK – Apparently, some people need to be reminded that Marc Anthony is an American.

The New York-born singer of Puerto Rican descent touted his roots Thursday on “Live with Kelly and Michael” after some people criticized his selection to sing “God Bless America” at this week’s Major League Baseball All-Star Game.

The Grammy-winning salsa star said that he heard people were questioning why a foreign-born person was singing the patriotic song. Anthony said he was born in New York and added: “You can’t get more New York than me.”