The properties to be acquired include assisted living, independent living, memory care and skilled nursing facilities spread across 29 states and encompassing 10,350 units. As part of the deal Seattle-based Emeritus, an operator of assisted living communities, will purchase nine remaining properties from Blackstone supported by $52 million in secured debt financing provided by HCP.

HCP, of Long Beach, Calif., said it will enter into a new agreement with Emeritus to allow that company to continue to operate the facilities that are being acquired. Emeritus has also committed to invest an additional $30 million to improve the real estate and operating performance of the portfolio.

Blackstone and Emeritus have owned the properties since 2010, buying them for $1.2 billion in a bankruptcy-assisted deal with Sunwest Management Inc. The joint venture in the years since has invested $42 million in capital improvements, which the companies say has helped raise the occupancy rates across the portfolio from 80% to 88%.

The sale is provides a nice windfall for Blackstone. The firm invested about $220 million in equity in 2010, according to a person familiar with the matter, positioning the firm to earn a 150% profit on the sale.

HCP said the purchase should contribute to its earnings immediately, and solidify its relationship with Emeritus.

"We are pleased to further expand our strategic relationship with Emeritus, one of our key, best-in-class operating partners," company chairman and CEO Jay Flaherty said in a statement. "The transaction further demonstrates our thesis of unlocking significant value for our operating partners through real estate driven transactions while providing our shareholders with attractive risk adjusted returns."

For Emeritus, the deal "will allow us to monetize our economic and promoted interests in the joint venture, immediately resulting in excess of $140 million of proceeds," according to CEO Granger Cobb. The deal also secures the company's place managing the communities on a long-term basis.

HCP said it plans to finance the deal in part by selling 22 million shares in an offering to be managed by Goldman, Sachs & Co.

A Skadden, Arps, Slate, Meagher & Flom LLP team including partners Joseph Coco, John Rayis, Peter Serating, Audrey Sokoloff and David Goldschmidt advised HCP on the acquisition and the stock sale.

Paul, Weiss, Rifkind, Wharton & Garrison LLP represented HCP on the acquisition.

Simpson Thacher & Bartlett LLP provided counsel to Blackstone.

--David Carey contributed to this report