There’s no longer any doubt: Lower Manhattan is back.

That’s the upshot of yesterday’s dramatic announcement that Conde Nast — one of the nation’s top media companies — has agreed to become the anchor tenant at 1 World Trade Center, leasing a million square feet in a deal worth $2 billion over 25 years.

That’s great news for New York — and a tremendous vote of confidence in the commercial rebirth of Downtown, where the deal is being described as some of the most important real-estate news of the last two decades.

Kudos to Conde Nast for making the commitment — and to the Port Authority, for getting the deal done.

It marks a tremendous vindication for those who waged the ongoing battle — despite years of delays and bureaucratic mismanagement — to rebuild the site that was devastated on 9/11.

Most important, Conde Nast’s presence will do much to make the area a true “world trade center” — without having to rely on pre-signed government agencies to fill up space.

Indeed, mere word that the company — publisher of such magazines as The New Yorker, Vanity Fair and Vogue — was considering relocating from its comfortable Midtown location was enough to attract other large firms to the area.

And that, in turn, is playing a key role in the diversification of Lower Manhattan beyond the financial-services industry and growing residential development.

“We built a new reality at the World Trade Center, and this transaction will be the exclamation point on that turnaround,” said PA Executive Director Chris Ward.

Again, congratulations to all.