Mayor Mamdani:

You were a month shy of 10 and living in New York City when 19 Al Qaeda hijackers took down the twin towers on Sept. 11, 2001.

That apocalyptic day has been imprinted on your memory since boyhood. Twenty five years later, as mayor of the City of New York, it’s your solemn duty to honor the 2,977 innocent victims of Islamist terrorism on that sacred site.

Public officials attend each year to bear witness and show their respects, not deliver self-important speeches. I’m heartened that, despite backlash from some 9/11 families, you’ll be in attendance for the 25th anniversary of the worst day on American soil.

Before deciding, you didn’t conduct a poll or hold focus groups. You didn’t listen to your DSA buddies or the kids from Commie Corner. You faced down a viral online petition signed by tens of thousands urging you to stay away. Good for you.

In fact, you’ve said you will “proudly honor the families, the survivors and first responders” by standing alongside them at Ground Zero. Your presence will reaffirm the city’s continued commitment to always remember and commemorate the somber tragedy. Like Dec. 7, 1941, Sept. 11, 2001 is a “Day of Remembrance.”

9/11 also happened in Shanksville, Pa., at the Pentagon and aboard four commercial aircraft. But it was Lower Manhattan that took the deadliest blow. That’s your turf.

As it does every Sept. 11, the world will be watching. Your appearance will be more than symbolic: It shall send a message of New York City solidarity. You represent eight million New Yorkers, not only those who voted for you. Christians, Muslims, Hindus and Jews. Black, white, Asian and Hispanic. Old and young. Rich and poor. Democrats and Republicans. All of us.

I represented Chris Ward, then-executive director of the Port Authority, during the rebuilding of Ground Zero. I watched the World Trade Center rebuilt from the rubble, one floor at a time, and led VIPs on tours of the site. It was the most moving experience of my life.

This is your big opportunity to pay tribute, to be a uniter, not a divider, on the day recalling the horrific events of a quarter century ago. Convey the dignity, unity and grace the occasion demands. No winning smile or social media.

Take your cues from First Deputy Mayor Dean Fuleihan, the clear-headed adult in your inner circle and City Hall’s institutional memory. He has the 9/11 frame of reference you need. Seek his wisdom and judgment.

Thank City Council Speaker Julie Menin and September 11th Families for Peaceful Tomorrows for defending you against anti-Muslim bigots pressuring you to not show up.

Study 9/11 anniversaries of years past. Watch videos of then-President George W. Bush’s rousing speech at Ground Zero on Sept. 14, 2001 and his stirring, ceremonial first pitch at Yankee Stadium before Game 3 of the World Series on Oct. 30, 2001. We were all American patriots, united in shared grief.

Like Bush, you’re doing the right thing, not the political thing. Observing the anniversary of Sept. 11 — especially the 25th — is non-partisan, non-ideological and apolitical. Follow the lead of Mayors Giuliani, Bloomberg, de Blasio and Adams before you. Be statesmanlike. And invite the first lady to join you.

Set an example for future mayors. Leaders lead. Block out the external noise and online chatter. Be fully present on the hallowed footprint of Ground Zero. But expect protesters. You can’t win ‘em all.

Seize the moment, Mr. Mayor.

Frydman is CEO of Source Communications LLC, a strategic communications firm in Manhattan.