The purchase marks another step in the famously-reclusive billionaire' s strategy to build a property empire through Pontegadea Inmobiliaria, one of the biggest property companies in Spain, and his holding company Pontegadea Inversiones.
The source said late on Friday that Pontegadea Inmobiliaria had bought the tower from Abu Dhabi tycoon Khadem al-Qubaisi, whose fund had exercised a last-minute purchase option from Spanish lender Bankia, its previous owner.
Pontegadea Inmobiliaria declined to comment on the reported purchase of the tower - known as "Cepsa Tower" after the oil refiner Cepsa that leases it - which along with three others dominates the skyline of Madrid's northern district.
Ortega has bought properties in London's Mayfair and Oxford Street, along with other properties in prime locations in New York, Madrid and Seoul. He rents out much of the space to Inditex stories like Zara, but also to rivals such as H&M.
Pontegadea Inmobiliaria booked assets of 6.06 billion euros at the end of 2015, up 8.3 percent from the previous year.
($1 = 0.8894 euros)
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