The Colony Group has agreed to turn a stake equaling 40% to 70% of its earnings over to Focus Financial Partners, but it is holding on to its independence and plans for aggressive growth.

The firms announced the deal Tuesday morning.

Boston-based Colony Group will become a partner with Focus Financial, bringing $1.3 billion in assets under management to the table. The companies did not disclose financial terms of the deal, which marks New York-based Focus Financial’s fourth so far this year. The investment in Colony Group brings Focus Financial’s total assets under management to more than $45 billion.

“Focus Financial offered us the right mix of cash and equity consideration, as well as a very attractive earn-out structure,” Michael Nathanson, president and chief executive officer of The Colony Group said in a telephone conversation. “We view it as an opportunity to share our tremendous investment management expertise with other partner firms.”

The Colony Group will also be able build equity in TCG Management, the entity formed as a result of the transaction.

TCG Management will manage everything about The Colony Group, from its historical business looking after its more than 800 clients -- including high-net worth individuals, families and institutions -- to higher aspirations.

Colony Group plans to expand from its existing Boston headquarters, plus offices in West Palm Beach and Naples, Florida, as well as Washington, D.C., to other regions in the U.S. The Colony Group will offer and receive expertise from in Focus Financial’s network of partner RIA firms around the country.

Down the line, TCG Management could function as a platform that offers useful services to other advisory firms, large or small, Nathanson said. Management at Focus Financial agreed.

“Colony is simply one of the best independent investment advisors in the market and we have thrilled to be partnering with them,” Rudy Adolf, founder and chief executive officer of Focus Financial said in a statement. 

After the transaction closes on Oct. 1, Kirby Hamilton Colony Group’s founder, will step down as chairman. That move accelerates a succession plan that had already been in place for several years, and reflects the fact that Hamilton had begun to step away from managing The Colony Group on a daily basis.

A three-member board will run TCG Management: Michael Nathanson, will become chairman; Stephen Sadler, will be president of Colony Wealth Management; and Elizabeth Talbot will be as executive director and chief market strategist.