In its colorful 40-year history, Prince Street bistro Raoul’s has seen it all — from the druggy 1980s, when it was a clubgoers’ mecca, to the 2014 launch of a buttery bar burger that Esquire magazine called the best in the US.

But for all the changes it’s lived through, until recently Raoul’s never offered one thing that long ago became common on every nearby block: brunch.

In the fall, it launched a brunch that quickly made the Soho institution nearly as buzzy on weekends from 11 a.m. to 2:30 p.m. as it is in the wee hours, packed with smartly dressed noshers who seem to hail from every corner of the tri-state area except Soho.

But Raoul’s is no Sarabeth’s. Don’t expect a torrent of fluffy-egg dishes. “Our chef, David Honeysett, and I wanted to avoid the eggs Benedict thing,” says manager Karim Raoul, 37, whose father and uncle, Serge and Guy Raoul, founded (and still own) the place. “We wanted something different — not completely traditional.”

The resulting lunch-brunch hybrid boasts a soufflé apple pancake that was worth waiting 40 years for, and a luscious smoked-salmon omelet that recalled a beloved favorite of mine at the original East 53rd Street Brasserie. Steak à cheval au poivre, a bavette cut, is a few ounces smaller than the dinner shell steak, and is crowned with a runny sunny-side-up egg.

But the star is Raoul’s instant-classic hamburger, which — unlike at dinner, when a mere dozen are available, and only at the bar — can be enjoyed at tables. “We have maybe 25 or 30 of them at brunch,” Karim says. The juice-oozing, au poivre-drenched Pat LaFrieda beef blend gives Minetta Tavern’s exalted Black Label number a run for its money — and, at $23, it’s $4 less than Minetta’s.

So far, the night and day crowds look remarkably alike, except for a nocturnal surfeit of men’s hats at the bar. This is not the Soho of the 1978 Jill Clayburgh movie “An Unmarried Woman.” Styles run more to Uniqlo and Lands’ End than to the artists-in-lofts look of long ago.

Noshers navigate a room that’s sexily snug and turns downright cramped. “It’s how I stay thin after [a big brunch],” a pretty young thing says of compressing herself to ascend the notoriously tight spiral staircase to the upstairs toilets.

The stairs, like the tile walls, coffered ceilings and black-and-beige booths, look unchanged since the room became Raoul’s in 1975 — and since it was an Italian place for many years before then.

Only the art is “new”: The sprawling image of a nude woman lying prone on a sofa has presided serenely over the front dining room since like-yesterday 1986.

Despite the instant popularity of brunch, Karim says there was no clamor for it from longtime customers. In fact, at first, “just the idea was a big adjustment for them, because we were always known as a night place,” he says.

And our waiter — a newbie with only four-plus years on the job — notes “the old guard [servers] held out” against brunch.

So what changed the owners’ minds? Was it the sight of crowds waiting at the Dutch across the street?

“It wasn’t just the Dutch,” Karim says. “I live upstairs. We own the building. And whenever I went out for my own brunch in the neighborhood, I’d have to wait an hour.”

Although Raoul’s has been part of the local fabric since Gerald Ford was president, it came alarmingly close to being home to a different animal altogether.

“When my father and uncle starting looking for a restaurant, this was the only one they really liked,” Karim says.

“But the previous owners were talking to Burger King. Fortunately, they said they’d prefer to sell it to someone who would keep it as it was.”

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