Pontegadea collects almost all of the dividends which Ortega earns - 1.6 billion euros in 2019 - and then re-invests the money in real estate, a spokesman for the holding firm said.
The 83-year-old stepped down as chairman of Inditex, the owner of Zara, in 2011 but he still owns 59 percent of the world's biggest fashion retailer, which also owns other popular fashion brands like Massimo Dutti and Bershka.
He is currently the world's sixth richest person, according to Forbes. His latest major real estate purchases came earlier this month when Pontegadea bought an office building used by Facebook in Seattle for $415 million (376 million euros) as well as the "Troy Block" complex in the same city which houses part of Amazon's headquarters for $740 million.
It is "normal" for entrepreneurs with a lot of capital to set up an investment fund to manage the cash to "diversify and preserve" the fortune by building a "refuge" from stock market fluctuations, Juan Carlos Amaro, a professor of finance at the Esade business school in Barcelona, told AFP.
Ortega, who founded fast-fashion giant Zara with his ex-wife Rosalia in 1975 in Spain's northwestern region of Galicia, fiercely guards his privacy and is known for being a prudent investor.
Analysts said he was targeting real estate as a long term investment, not to speculate.
"It is a very conservative activity which was chosen, not for its great profitability but because it is sufficiently stable," a Pontegadea spokesman said.
Ortega steers clear of housing real estate, which is potentially more profitable but has a bad reputation after a property bubble burst in the late 2000s, triggering a prolonged recession.
His portfolio is mostly made up of offices and shops, as well as some hotels.
In addition to owning several buildings in Madrid and Barcelona, Ortega has become the main real estate proprietor of London's Oxford Street, Europe's busiest shopping street. Last year Pontegedea made a rare venture outside of real estate, snapping up 10 percent of Telxius, Spanish telecoms giant Telefonica's subsidiary which provides telephone towers and fibre networks in Europe and Latin America.