Halcyon House in 1965. (Harry Naltchayan/The Washington Post)

(**Updated, Tuesday 4:30 p.m.: Halcyon, Evermay buyers want to preserve historic homes ** )

The pool of potential buyers for eight-figure mansions is relatively small in Washington. So who, many wondered, could possibly buy Georgetown’s second-most expensive house of 2011, once biotech tycoons Ryuji Ueno and Sachiko Kuno had already bought the most expensive?

Answer: Ryuji Ueno and Sachiko Kuno.

Yes, indeed, the husband-and-wife scientists behind Bethesda’s Sucampo Pharmaceuticals have done it again. The Georgetowner reported Monday that Ueno and Kuno are the mystery buyers who took historic Halcyon House off the market last week for $11 million — four months after they purchased the fabled Evermay estate for $22 million.

A bedroom at Halcyon House, 2008. (Bob Narod)

If you’re wondering why they need two big homes in Georgetown, well, records show they already have another in the neighborhood, as well as three mansions in Potomac, two on the Eastern Shore and a condo in NYC.

And they clearly have an eye for a bargain: The 225-year-old Halcyon House — built by Navy Secretary Benjamin Stoddert — was originally listed for $30 million when the Dreyfuss family put it on the market in 2008. It had dropped to $15 million by early this fall, and to $12.5 million before Ueno and Kuno pounced.

Evermay — like Halcyon, a popular venue for high-end weddings — lingered on the market just about as long, with the price cut more than 50 percent from its initial asking of $49 million. Its final sale price of $22 million was just below the citywide record price of $24 million that the Bowie-Sevier home fetched in 2007.

The new most-expensive Washington home currently on the market? Former Pakistani Prime Minister Moeen Qureshi’s Massachusetts Avenue Heights mega-villa — $12 million.

Update, 11/22: Halcyon buyers want to preserve historic home

Read earlier: Georgetown mansion Evermay purchased by biotech entrepreneurs, 7/25/11

Family’s hidden history revealed after sale of Evermay, 9/28/11

Centuries of drama at Halcyon House (photos), 8/30/08

updated Tuesday 12 p.m.