Related Beal, the Boston-based real-estate development arm of New York’s Related Cos., on Monday formally proposed a 1.1 million-square-foot mixed-use development adjacent to the Gillette World Shaving headquarters in South Boston.

Related Beal acquired 6.5 acres of surface parking lots from The Procter & Gamble Co., which owns Gillette, this spring for $218 million and tapped architecture firm Kohn Pedersen Fox Associates to develop a master plan.

In a Nov. 18 letter of intent to the Boston Planning and Development Agency, Related Beal President Kimberly Sherman Stamler said the company is planning three buildings:

• A 366,000-square-foot, 180-foot residential building;

• A 344,000-square-foot, 180-foot office; and

• A 400,000-square-foot, 123-foot lab/research and development building.

The letter of intent is the first step in formally pitching a project to city planning and development officials.

In the letter, Stamler emphasized the project’s focus on sustainability and resiliency, and said the project will work “in concert with other city, state and federal agencies to provide area-wide flood protection as part of the Climate Ready South Boston Initiative.”

“In parallel, we look forward to working with the BPDA, Sasaki and our Fort Point neighbors in effectuating the development and programming of the significant open spaces that will be created as part of the Project,” Stamler said. “These open spaces will achieve the dual goals of being both accessible as well as adaptive and resilient, and will provide meaningful equitable and public connections within Fort Point, to the Harborwalk and beyond.”

Related Beal anticipates developing the three buildings simultaneously and having buildings ready for occupancy by mid-2024.

Related Beal’s acquisition followed a string of smaller land deals between P&G (NYSE: PG) and real-estate development firms. Gillette, which Cincinnati-based consumer products company P&G acquired in 2005 for $57 billion, had closely guarded its 44-acre South Boston campus for close to a century. But P&G has sold off increasingly larger portions of the campus for increasingly larger sums, such as a 30,000-square-foot building and quarter-acre parking lot for $11.5 million, and a 2.5-acre parcel on Necco Street for $83 million.

The selloff has prompted a wave of life-science development proposals. What’s more, P&G earlier this month said it has launched an assessment of it South Boston and Andover properties as part of a study “to define the best way to structure our business operations for success for the next century to come.”