The Waldorf-Astoria Hotel’s September reopening, five years later than first planned, will be well worth the long wait.

The magnificently restored Waldorf-Astoria marks the return of the Big Apple’s “grand hotel” style, featuring splendid public spaces open to all, befitting the establishment’s iconic heritage.

New York City’s great hotel lobbies fell one by one over the decades. Even the Plaza’s once-spectacular entrance is a shadow of its old self.

In contrast, the Waldorf’s public areas are so extensive that it’s easy to forget more than half the building has been transformed into condo apartments. The hotel went from 1,400 guest rooms down to 375, but these are much more spacious than before.

The Waldorf was a venue for notable figures such as Marilyn Monroe, Grace Kelly, Frank Sinatra, and global royalty. It played a vital role in the city’s celebratory culture for nearly a century.

But after it closed in 2017, relaunching it fell far behind schedule due to construction issues, COVID-19 and an unexpected change in Chinese ownership.

The many delays that The Post first reported will be forgotten when visitors have their first look at the ground floor opening this week, before the first room guests arrive on Sept. 1.

The new Waldorf-Astoria, an Art Deco icon of New York City since 1931, is a sight to behold. Its landmarked lobby and Peacock Alley lounge between Park and Lexington avenues never looked so beautifully burnished since I first saw them a half-century ago.

Two gorgeous new restaurants, a magnificent marble floor and a welcoming porte-cochere entrance on East 49th Street elevate the Waldorf to a higher realm than the faded, tourist-trampled inn of the recent past.

Fears that 19th Century murals and other interior details would be lost turned out to be baseless. All were meticulously restored by project architect Skidmore, Owings & Merrill and interior designers Pierre-Yves Rochon and Jean-Louis Deniot under the watchful eyes of the Landmarks Preservation Commission.

The famous floor mosaic “Wheel of Life” near the Park Avenue entrance is so perfectly restored, it looks as France’s Louis Rigal assembled its 148,000 pieces this year rather than in 1931.

Much of the vast ground floor was reconfigured to improve sightlines. The check-in counter that forced Peacock Alley revelers to stare at piles of luggage was relocated. Gone are old lounges such as notoriously tacky — and sometimes scandalous — Sir Harry’s Bar.

Peacock Alley’s walls in dark maple and black marble columns are magically lighter on the eyes than previous blue panels. The Waldorf clock, commissioned by Queen Victoria in 1893, was cleaned and polished to look new.

Composer Cole Porter lived at the Waldorf, where he composed Broadway hits like “Anything Goes.” His Steinway piano reposes serenely in the lobby where waitstaff sport outfits by designer Nicholas Oakwell — with silver silk blazers and waistcoats for women, three-piece check suits for men.

The restaurants are a special pride of hotel managing director Luigi Romaniello. Lex Yard, a plush, two-level affair helmed by Gramercy chef Michael Anthony, opens on a limited basis for dinner tonight.

Japanese cafe Yoshoku will open in stages as well. The Peacock Alley bar’s cocktail menu was devised by Jeff Bell of downtown Please Don’t Tell fame.

There’ll be live music, Romaniello said — “nothing intrusive, maybe jazz.” I hope he sticks to that. Peacock Alley’s enchanting surroundings don’t need a cabaret to transport guests to heaven.