Atlas Merchant Capital, the firm Diamond co-founded in 2013 after his departure from Barclays, will buy a 19.7 percent stake, while Edmond de Rothschild will take 8 percent.

Kepler added it was counting on its new partners to help it keep growing through acquisitions, and did not rule out looking for potential targets in the United Kingdom once Brexit terms were clearer, or in the United States.

Kepler, which has grown rapidly over the past 10 years through purchases and partnerships with large European banks such as Italy's UniCredit, also said it could ultimately carry out an initial public offering (IPO) within the next five years.

"It's not unthinkable, it's part of our plans," Laurent Quirin, the chairman of Kepler's supervisory board, told reporters. "We'd need to keep on growing at a good pace."

Kepler did not give financial details of the transactions.

As the new investors come in, French-based private equity fund Blackfin Capital Partners, which held 19.7 percent, and French bank Credit Mutuel ARKEA, which held 4.2 percent, will sell out of their current holdings.

The company's management will reduce the stake it holds collectively to 25.5 percent from 31.9 percent, although they will keep 40 percent of the voting rights.

UniCredit, meanwhile, will raise its stake in the brokerage to 10.3 percent from 5.2 percent, while French state-owned investment fund Caisse des Depots et Consignations (CDC) will trim its holding to 5.2 percent from 7.8 percent.

Since Kepler's management bought out the company in 2009, its revenue has jumped fivefold, reaching 252 million euros (222.34 million pounds) in 2017. It is expected to hit 270 million euros this year with a 40 million net profit, Quirin said.

(Reporting by Inti Landauro and Matthieu Protard; Editing by Sarah White/Sudip Kar-Gupta)

By Inti Landauro and Matthieu Protard