Private equity firm Carlyle Group is set to acquire a significant minority stake in Europe's largest privately-owned oil and gas company, Cepsa, from Abu Dhabi sovereign wealth fund Mubadala.

The Washington, D.C., based firm, one of the largest asset managers in the world with $216 billion in assets, plans to buy a 30-40% stake in Cepsa, or Compañía Española de Petróleos, S.A.U, which it values at $12 billion. That means the stake could be worth as much as $4.8 billion.

Mubadala will remain the majority shareholder, and the transaction's completion is expected by the end of 2019, subject to regulatory approvals.

The news follows a cancelled IPO (initial public offering) last year by Mubadala of a 25 percent stake in Cepsa, which was shelved amid last October's stock market rout.

"We found Cepsa very attractive to invest in," Marcel van Poecke, head of Carlyle International Energy Partners, told CNBC's "Street Signs" on Monday.

"In general, IPO markets in Europe — especially for industrial companies like Cepsa, but also other companies — were not good last year."

"We invest private capital over many years in companies, so we have a very outspoken idea about value and how we can create more value … We are not susceptible to day-to-day or month-to-month movements in market prices and I think that is important," van Poecke said.