Russian billionaire Roman Abramovich loves the Big Apple so much that he’s buying up most of a city block to build one of New York’s largest mansions.

The oligarch, who Forbes estimates is worth $9.3 billion, plans on building a dream mansion to live in with his glamorous girlfriend, Dasha Zhukova, the mother of two of his seven children.

Abramovich, who went from orphan to steel magnate, secretly purchased 11 E. 75th St. — a narrow, 21-foot-wide, 9,495-square-foot town house — for $29.7 million from developer Larry Gluck in October.

His lawyer, listed on the property records as Evan Levy, did not return calls, nor did Abramovich’s spokesman.

In December, Abramovich secretly bought another town house, two doors down, at 15 E. 75th St. That was an even tinier, 17-foot-wide house, for $18.3 million. That home is 7,286 square feet.

In between sits 13 E. 75th St., which is currently owned by Mark and Lori Fife — who are in contract, a source said, to sell it to a “Russian” mystery buyer.

That town house is also 17 feet wide. Fife, who is the founder of En Trust Capital, bought the home in 2000.

At the time, it was on the market for $7.4 million. Today, it would be worth around $20 million — and far more if the sellers knew the buyer had already closed on its neighbors, sources said. Fife did not return calls for comment.

Abramovich previously was set to pay what then would have been a record $75 million for a co-op in the Berwind mansion at 828 Fifth Ave. But the wealthy widow who owned it turned him down — convinced she could get more.

Gluck told The Post he thought it was “super cool” Abramovich bought his town house.

The sellers of the town houses on East 75th Street did not know that Abramovich was the buyer.

“They just got a knock on their door one day and thought a rich Russian wanted to buy their town house.

Had they known who it was and what he planned on doing, they would have asked for a lot more money,” a source said.