(CNN) First lady Melania Trump announced on Tuesday afternoon that she had -- ceremonial shovel in hand -- marked the start of construction for a new White House tennis pavilion on the South Lawn.

"Exciting to break ground on the new tennis pavilion project at the White House today," she tweeted. "Thank you to all who will help in making this legacy piece possible for future first families to gather at and enjoy for years to come."

There has been no previous news of the new pavilion from the White House, nor of its projected existence, but in June the National Park Service -- which operates the 18-acre grounds of the White House -- submitted a proposal about the structure and its construction to the National Capital Planning Commission.

The proposal described a two-phase plan. According to the proposal, the first phase will "replace a small building that currently houses a restroom and a storage space on the White House grounds just southwest of the White House itself." The second phase will involve replacing a maintenance building dubbed "The Pony Shed," which is used by National Park Service workers.

The first lady's tweet included three photos of her in a navy coat and her signature high heels, shaking hands and smiling with a group of people. One of the images shows President Donald Trump from behind, also greeting the group, who are not identified.

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