Back in the day, the late photojournalist Ken Regan — known for his photographs of sports, film and rock stars, including The Beatles, The Rolling Stones, Bob Dylan, Bruce Springsteen and Jimmy Hendrix — worked out of a massive 4,200-square-foot commercial space at 6 W. 20th St., which is now an 11-story co-op building, in the heart of the Flatiron District.

While the space is currently zoned commercial, a mystery buyer has purchased the space and will be converting it to a residential loft with three to four bedrooms and bathrooms.

The unit was asking $4.65 million and sold for around $4.5 million.

The listing broker was Robert Dankner, president of Prime Manhattan Residential.