Kate Middleton and Prince William got together with Brooklyn’s own royal couple Monday night, meeting courtside with Jay Z and Beyoncé at Barclays Center during a Nets game.

The Duke and Duchess of Cambridge walked into the arena to a standing ovation, and later greeted the pop queen and hip-hop king at halftime.

“Good, really good,” William said about their experience at the game. “It was our first time.”

After the royal duo met the Brooklyn power couple, they enjoyed popcorn and watched the Cleveland Cavaliers and LeBron James trash the Nets, 110-88.

“King James’’ was honored to meet the royals and gave them a jersey for their son, George, and cupcakes from his hometown.

“I thanked them for coming here to America to watch our game,” James said. “For them to take time out of their busy lives to come here, it means a lot to our sport.”

Earlier in the day, Kate dazzled a group of East Harlem kids who thought she was Princess Elsa from the movie “Frozen’’ — even if she didn’t have a tiara.

“She didn’t have a crown,” lamented Andrew, 4, after meeting the Duchess of Cambridge at the end of her visit to his day-care facility, the Northside Center for Child Development.

But Kate was still the kids’ favorite royal, as her hubby, William, hobnobbed with President Obama and other dignitaries in Washington, DC.

“Do you know who’s coming to visit today?” a school administrator asked pupils as Kate walked in.

“Princess!” a girl named April shouted.

Rose Ann Harris, a school director, later explained, “They thought [the duchess] was the princess from ‘Frozen.’”

Mila, a 6-year-old student, got a hug from the five-months-pregnant Kate after handing her a bouquet of red roses at the East 111th Street center.

“I gave her flowers. It was amazing,” Mila gushed.

Little Andrew, who gave city first lady Chirlane McCray roses as she left with Kate, said he “felt happy” about meeting the duchess.

During his busy day, William also met first with Vice President Joe Biden and discussed international efforts to destroy the terror group ISIS, Britain’s Mirror newspaper reported.

William later took a seat alongside Obama in the Oval Office, where reporters were warned not to take selfies with the royal.

The prince joked with Obama that during the “chaos” of his son George’s birth, he forgot to ask whether his firstborn was a boy or girl. He added that he and Kate don’t want to know the gender of their baby on the way.

William gave the president a customary signed portrait of himself, a Kensington Palace representative said.

But it was Kate who won over the crowds, stepping out in Manhattan wearing a black coat from the tony British brand Goat along with black tights and black heels.

“Your royal highness!” a crowd of admirers shouted as Kate was greeted at Northside with a handshake by McCray, clad in the purple Nanette Lepore coat she wore at Mayor Bill de Blasio’s inauguration.

During her visit to the preschool, Kate wrapped gifts for a Santa exchange for the kids, using green-and-red teddy-bear paper to cover a singing butterfly.

“[The duchess] did take time to painstakingly make sure it was beautifully wrapped,” said Nina Fenton, the development director at Northside.

Kate ate lunch at the British consul general’s residence, feasting on a pressed vegetable terrine, poached salmon with lemon pearl barley risotto, and an apple and rhubarb crumble.

She and her husband met back up at their Upper East Side hotel, The Carlyle, by 4 p.m., then left to rub elbows with Hillary and Chelsea Clinton at a reception, again at the British consul general’s residence, co-hosted by the Royal Foundation and the Clinton Foundation.

On Tuesday, the couple is set to visit the 9/11 Memorial and a star-studded fundraiser at the Met to raise scholarship money for the University of St. Andrews, the Scottish school where they met.

Additional reporting by Tara Palmeri, Leonica Valentine. Kathleen Culliton and Geoff Earle