DoubleLine Capital, an investment management firm headed by billionaire Jeffrey Gundlach, is expanding its headquarters in downtown L.A.’s Wells Fargo Center.

The firm signed an 11-year lease expansion deal with downtown’s biggest office landlord, Brookfield Property Partners, increasing the space it takes at Wells Fargo Tower North by 40 percent to 52,000 square feet. The lease is valued between $25 million and $30 million, according to industry sources.

David Toomey and Brian Davies of tenant brokerage firm Cresa Los Angeles represented DoubleLine in the deal, which closed last week, at the 1.4 million-square-foot Class A office building at 333 S. Grand Ave. Brookfield was represented in-house by Senior Vice President John Barganski and Vice President James Malone.

Toomey said the expansion was necessary because the firm has seen a dramatic inflow of capital in the last year or so, a boom stimulated by clients reinvesting money pulled from Pacific Investment Management Co. after “bond king” Bill Gross announced his departure. With more clients, of course, come more employees.

Barganski said the lease indicates good news for downtown.

“It’s another major financial firm making an expansion and long-term commitment not only to the property but to Bunker Hill, where traditional financial firms have headquartered in Los Angeles,” he said. “It’s a huge win because we expect that this expansion will be compounded by additional expansion by DoubleLine over the term of the lease.”

DoubleLine has been in the north tower of Wells Fargo Center, which consists of two buildings connected by a three-story glass atrium, since it was founded five years ago. The north tower is 83 percent occupied with a tenant roster that includes Wells Fargo & Co. Bank and the headquarters of Oaktree Capital Management, an early DoubleLine backer.

“The partners chose the Bunker Hill neighborhood of downtown Los Angeles as the place to start our business,” said Henry Chase, chief financial officer of DoubleLine. “We are pleased to expand and continue our operations in the building where we began.”