The seller is a joint venture of Blackstone Real Estate Partners II and Glenborough Realty Trust, a San Mateo-based REIT. Blackstone owned a 90% stake in the property and Glenborough the remainder. The buyer is believed to be Beacon Capital, a Boston based investment advisor but that could not immediately be confirmed Tuesday morning because Glenborough CFO Brian Peay did not make himself available for comment, Beacon Capital senior managing director Jeremy Fletcher was on a plane and a Blackstone representative could not immediately respond.

Glenborough said in a prepared statement that its share of the gain from the June sale was approximately $9.5 million, which equates to an internal rate of return in excess of 20% to all investors. The sale was prompted by the renewal of one of the major office tenants and the potential to convert the multifamily units to condominiums, the company said.

The property was developed in 1988. In April 1999, Glenborough purchased a 10% interest in a joint venture holding the fee simple title to the land under Rincon Center I & II. The land was purchased from the United States Post Office for a purchase price of $80.5 million, according to SEC filings. At that time, the land had a triple net ground lease with a remaining term of 51 years with minimum 30% rental increases every six years.