Harper’s Magazine owner John R. “Rick” MacArthur tapped insider James Marcus to take over as the new editor-in-chief of the magazine, replacing Christopher Cox, who was forced out in early February after only three months on the job.

Marcus declined to comment on the past “editorial differences” that were blamed for the Cox/MacArthur blowup. Cox was also an insider who had succeeded Ellen Rosenbush.

She was brought back on an interim basis after the Cox ouster.

“It’s a thrilling day for me,” said Marcus, who had joined the magazine in 2010 as a deputy editor to Rosenbush.

He said he did not ask for or receive a long-term contract. “It was just a handshake,” said Marcus, who had been Amazon employee number 55 and authored a book, “Amazonia,” about his five years working there in the early days.

One of the reasons for the clash between Cox and MacArthur, sources said, was differences over plans to redesign the cover. Yet the cover over the past several issues has been redesigned.