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Boxing legend Muhammad Ali died of septic shock after spending five days at an Arizona hospital for what started out as respiratory problems and gradually worsened, succumbing only after his wife and children arrived at his bedside to say goodbye, a family spokesman said Saturday.

"It was a solemn moment," Bob Gunnell told reporters in Phoenix.

The details came as Ali's family revealed plans for a Friday funeral in his hometown of Louisville, Kentucky, a daylong affair that will include a procession through the streets where the 74-year-old world champion grew up and learned to box. His body is expected to be returned to the city within two days.

Related: Muhammad Ali, 'The Greatest of All Time', Dies at 74

The service will include eulogies from former President Bill Clinton, journalist Bryant Gumbel and comedian Billy Crystal. He'll be buried in a local cemetery with only family watching.

In preparation, Louisville lowered flags in mourning on Saturday as it looked toward Ali's final homecoming.

Outside the Muhammad Ali Center, locals created an impromptu memorial, leaving flowers and written tributes.

A few blocks away at Louisville Metro Hall, Mayor Greg Fischer marveled at the many outsize roles Ali embodied: sports champion, civil rights icon, humanitarian and "interfaith pioneer."

Louisville Mayor Greg Fisher addresses a gathering of supporters and mourners of Muhammad Ali from the steps of the Louisville Metro City Hall on June 4, 2016, in Louisville. Timothy D. Easley / AP

"The 'Louisville Lip' spoke to everyone," Fischer said, referring to the dismissive nickname the press gave the boastful Ali early on his career. "But we heard him in a way no one else could, as our brother, our uncle and our inspiration."

Ali, who had suffered for more than three decades from Parkinson's disease, had survived several death scares in recent years, so when he was admitted Monday with breathing problems his family expected him to rebound, Gunnell said.

Then things turned serious, and it became clear that he wasn't going to improve.

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Photos: Float Like a Butterfly: Muhammad Ali's Life in Pictures

His family traveled to his bedside, where they remained for about a day before Ali died at 9:10 p.m. local time on Friday. The official cause of death was "septic shock due to unspecified natural causes," Gunnell said.

Septic shock refers to an aggressive, full-body inflammatory response to an infection, and is common among the elderly and those with weak immune systems. The blood pressure plummets, leading to organ failure.

NBC News Medical Contributor Dr. Natalie Azar said it is not surprising that Ali’s respiratory ailment led to sepsis considering his age and longtime battle with Parkinson’s. “Any chronic illness like that makes you less able to deal with a huge insult like an infection," she said.

Azar added that sepsis is usually not painful.

One of Ali's daughters, Hana Ali, recalled his final moments with family by his side, hugging and kissing him and holding his hands as they chanted Islamic prayers.

"We all tried to stay strong and whispered in his ear, 'You can go now. We will be okay,'" Hana Ali wrote on Twitter.

Even after many of his organs failed, his heart kept beating for 30 minutes, she wrote.

Ali grew up on Grand Avenue in a middle-class but segregated section of Jim Crow-era Louisville, and was inspired to box at 12 by a police officer who heard him ranting about someone who'd stolen his bicycle. The racism he absorbed there as a child influenced the political stands he made years later. But he continued to return to Louisville as his legend grew, and the city embraced him as a son.

At the Muhammad Ali Center on Saturday, CEO Donald E. Lassere read a statement from the institution, which said Ali "will be remembered for his love for all people, his athleticism, his humanitarian deeds, social justice and perhaps mostly his courage in and out of the ring."

Lassere added, "And I'm sure Muhammad would want me to say this as well: he would want to be remembered for how pretty he was."

Fischer asked his audience outside Metro Hall to imagine what it must have been like to witness Ali, born Cassius Marcellus Clay Jr. in 1942, as an infant — his long, remarkable life still ahead of him.

"Imagine that day, that little boy, eyes wide open, looking around the the room at the old Louisville General Hospital, not knowing the life that awaited him, the life he would make, the world he would shake up, and the people he would inspire," Fischer said. "And like you, I am absolutely one of those people."

The mayor added: "Muhammad Ali belongs to the world, but he only has one hometown."

To accentuate that point, Fischer pointed out some of the many honors and titles Ali accrued in his post-boxing career: Amnesty International lifetime achievement award, Presidential Medal of Freedom, Sports Illustrated's Sportsman of the Century, and co-founder, with his wife, Lonnie, of the Muhammad Ali Center, created to "promote respect, hope and understanding in Louisville and around the world."

Muhammad Ali attends the 2014 Muhammad Ali Humanitarian Awards at the Louisville Marriott Downtown on Sept. 27, 2014 in Louisville, United States. Stephen J. Cohen / Getty Images, file

Earlier on Saturday, a spokesman for Ban Ki-moon, secretary general of the United Nations, which named Ali a "messenger of peace" in 1998, called him "a world champion for equality and peace."

"Muhammad Ali belongs to the world, but he only has one hometown."

The spokesman recalled Ali first connecting with the U.N. in the 1970s to campaign against apartheid and racial injustice. Later, Ali traveled the world for the U.N. to support children's initiatives and racial and political reconciliation.

"The United Nations is grateful to have benefited from the life and work of one of the past century’s great humanitarians and advocates for understanding and peace," the statement said.

Years before his death, Ali outlined to his family how he wanted it to be marked. Friday's funeral will follow those wishes, Gunnell said.

The event will begin with a morning procession through the city, passing locations that were "historically important to Muhammad,' his family said in a statement. That will include his old neighborhood, a street named after him, and spots on Broadway where many iconic photos were taken of him after he returned from the 1960 Rome Olympics with a gold medal, Gunnell said. As Ali wanted, the procession will move slowly to allow mourners to pay their respects, he said.

The funeral itself will be held at the KFC YUM! Center, a 22,000-capacity sports arena and will be open to the public. It will be led by an imam in the Muslim tradition, but it will also embrace elements of other religions, including a variety of clergy, Gunnell said.

"It's important for them to have a memorial service open to people of all walks of life," he said of Ali's family.