They’re not dissing Third Avenue anymore.

Reflecting the corridor’s rising fortunes after years of “Third’s the Bird” jokes, the redevelopment of 850 Third has added a tasty side dish to its $80 million menu of inside-and-out repositioning. 

Waterman Interests and HPS Investment Partners, owners of the mostly vacant, 605,000 square-foot Midcentury tower between East 51st and 52nd streets, signed a big-league restaurant even as work continues apace to re-launch the refreshed property by the end of the year.

The rebirth of 850 Third comes after companies left the avenue for more modern and glamorous locations on Park Avenue, Sixth Avenue and the far West Side. The avenue’s recent resurgence includes huge conversion projects that are eliminating obsolescent offices and will soon draw more residents.

Kellari Hospitality Group, owner of popular Kellari Taverna on East 44th Street since 2005, will launch a ground-level, 4,500-square-foot Greek and Mediterranean eatery called Artemis, as well as a private dining room below grade.

Kellari owner Stavros Aktipis called the 850 Third Ave. location a “unique convergence of business, residential and lifestyle audiences. The concentration of nearby office buildings make it a natural hub for business  lunches, corporate dining and after-work gatherings.”

The deal adds a touch of public glamour to 850 Third Ave., a 21-story tower that typifies the avenue’s ongoing revitalization.

The building’s comprehensive redevelopment includes all-new lobby, elevators, HVAC and other mechanical systems. A transformed facade by Dan Shannon of MdeAS Architects, who helped redesign Vornado’s 2 Penn, boasts new, double-pane windows and spandrels will lighten the structure’s now-dark appearance and “make it look completely different,” said Waterman managing director Simon Wasserberger, who’s in charge of the project. The facade work is to begin soon.

Wasserberger noted that availability at 850 Third includes Midtown’s largest block of contiguous space — some 450,000 square feet on floors 3-17. Leasing agent JLL will seek to lure private-sector service firms from fields such as law, insurance and accounting.

Right across the street from 850 Third is another Midcentury office property, 845 Third, which Israeli billionaire Idan Ofer bought earlier this month with plans to convert it into 529 rental apartments.

MetroLoft is converting the former Pfizer headquarters at 42nd Street, and SL Green will break ground on its conversion of 750 Third Ave. this year.

Major recent office leases were led by Bloomberg LP’s 925,000 square-foot expansion and renewal at 919 Third Ave. and Kirkland & Ellis’s new lease at 900 Third Ave 

New restaurants will soon include downtown favorite MAMO at the Lipstick Building.