World leaders, dignitaries, and thousands of mourners have begun arriving at St. Peter's Square in Vatican City to pay their final respects to Pope Francis.

U.S. President Donald Trump, former President Joe Biden, U.K. Prime Minister Sir Keir Starmer, and the Prince of Wales are among the high-profile attendees at the Requiem Mass, which begins at 9 a.m. UK time.

French President Emmanuel Macron, Irish President Michael D. Higgins, and Ukrainian President Volodymyr Zelenskyy are also in attendance. Zelenskyy arrived earlier on Saturday morning alongside his wife, Olena Zelenska, following uncertainty caused by recent air strikes in Kyiv that had disrupted his travel plans.

An estimated 500,000 people are expected to gather for the open-air funeral service.

Pope Francis, who passed away at age 88 on Monday—just hours after addressing the public during Easter celebrations—had been lying in state in St. Peter’s Basilica for three days. Approximately 250,000 mourners filed past his body before his coffin was sealed in a private ceremony on Friday.

Nuns gathering in the square ahead of the service described the late pontiff as a “saintly man… a man of peace, who wanted peace for the whole world,” according to the Associated Press.

Sister Nilma Navarro from the Philippines said Pope Francis was “the most humble person I have ever met,” adding that he served as a shepherd not only for Catholics but also embraced people of other faiths.

“He was a very charismatic pope, very human, very kind,” said Miguel Vaca, a pilgrim from Peru, who had lined up from 7 a.m. to gain entry into the square.