New Owner of Cassini Family's Former Mansion Files $5M Permit

A limited liability company that paid $34.5 million for a landmark Upper East Side mansion tied to the Cassini fashion family has filed a $5,027,400 permit to gut it back into a single-family house, according to city construction and property records reviewed by The American Developer.

Why it matters

The townhouse at 15 East 63rd Street was long associated with designer Oleg Cassini and, after his death, with Marianne and Peggy Nestor, the stepdaughters who fought creditors and each other over the property for more than a decade before Peggy Nestor’s estate landed in Chapter 11. ACRIS records show Albert Togut, the Chapter 11 trustee, and the Estate of Peggy Nestor deeded the building to 63rd St Townhouse LLC for $34,500,000 on March 17, 2026, closing out one of the Upper East Side’s longest-running ownership disputes. A companion satisfaction of mortgage recorded the same week releases Marianne Nestor and Peggy Nestor from an Emigrant Bank loan on the address, clearing the title the new owner now controls. The buyer wasted little time: the DOB filing proposes stripping the six-story building from five dwelling units back down to one, the kind of full de-conversion that only pencils at mansion-level budgets.

The numbers

The Alteration CO application, filed under job number M01439528-I1 through architect Tom Kundig of Seattle firm Olson Kundig, carries a reported construction cost of $5,027,400 across 16,758 square feet of work. The scope covers a change in use from a multiple dwelling to a single-family residence, removal of the existing sixth floor, and structural, mechanical, plumbing and sprinkler work, with the filing moving into Plan Examiner review on September 25, 2026. Combined with the March deed, the two records put roughly $39.5 million of recorded price and reported construction cost against a single Upper East Side address inside one calendar year.

What’s next

The filing has not yet reached permit issuance, so construction has not begun. This article will update if 63rd St Townhouse LLC’s ownership resolves to a named individual as the permit and any later filings progress. The sale closes out a long-running fight over one of the New York market’s more storied Upper East Side addresses, the kind of estate-driven mansion turnover the desk is tracking across Manhattan’s townhouse row.