Israeli billionaire Raz Steinmetz is a quiet investor in 15 Manhattan properties owned by Kushner Companies .

Steinmetz, who hails from one of Israel’s richest families, has been working with Kushner since at least 2012, Bloomberg reported. The Downtown Manhattan properties they jointly own are worth $150 million and the two sides also partnered on the Trump Bay Street project in Jersey City, according to Bloomberg.

The Steinmetz family made its fortune in the diamond trade. Raz’s uncle Beny, a diamond trader, has been under criminal investigation in the U.S. for allegedly bribing Guinean officials in exchange for mining rights.

Ethics experts told Bloomberg that the fact that Kushner’s links to Steinmetz haven’t been publicized until today highlights weaknesses in federal disclosure rules, which allow investors to remain anonymous behind shell companies.

Gaia Investment Corp., which Steinmetz controls with Shlomo Meichor and Assi Arev, bought a building on its own – a 150,000-square-foot Williamsburg loft building at 475 Kent Avenue – for $56 million.

In 2013, Gaia Investment Corp. and Kushner flipped six Manhattan buildings to a joint venture between Kushner and asset management firm Stonehage Fleming, making at least $4 million in profits.

“Kushner Companies has a longstanding relationship with Raz Steinmetz and Gaia, who have been terrific partners,” a Kushner spokesperson told Gaia. [Bloomberg] — Konrad Putzier