Kicking off his speech, King Charles thanked the American people for being welcomed during the semiquincentennial year of the Declaration of Independence. The remark prompted a huge applause from attendees.

"For all of that time, our destinies as nations have been interlinked," he said.

King Charles and Queen Camilla entered the House chamber to a standing ovation. The applause continued as the two walked down to the dais.

Lawmakers from both sides of the aisle are filling up the House chamber, with the excitement of a joint meeting in the air as guests begin to take their seats and wait for the House Sergeant at Arms to announce the arrival of King Charles and Queen Camilla.

Hundreds of ticketed guests have crowded the House gallery, giving the event the feeling of a State of the Union address -- absent the president. Each member of Congress was given one ticket to give to a constituent or special guest.

Atop the speaker's rostrum, Vice President JD Vance and House Speaker Mike Johnson chatted while dignitaries filled the room.

Former Speaker Nancy Pelosi, wearing a lavender suit in the chamber, was also present when Queen Elizabeth gave her 1991 address to Congress.

-ABC News' John Parkinson, Rachel Scott and Lauren Peller

King Charles will soon deliver a joint address to Congress, a key moment of his four-day state visit. The last British royal to speak to a joint session of Congress was Queen Elizabeth II in 1991.

There will be plenty of pomp and show surrounding the king's speech, including a bipartisan escort committee that will trail him as he makes his way to the speaker's rostrum. Supreme Court justices, the diplomatic corps and president's Cabinet are all invited to attend as well. Vice President JD Vance is expected to sit alongside Speaker Mike Johnson atop the rostrum.

During the joint meeting, members of Congress may try to "hog the aisle" to get a moment gripping and grinning with the king.

Read more about the upcoming speech here.

-ABC News' John Parkinson and Lauren Peller

Amid diplomatic tension between the U.S. and the U.K. over the war in Iran, President Trump spoke about the "special relationship" between the two nations.

"In the centuries since we won our independence, Americans have had no closer friends than the British," Trump said. "We share that same root. We speak the same language, we hold the same values, and together, our warriors have defended the same extraordinary civilization under twin banners of red, white and blue."