Hero Bravest Timothy “Timmy” Klein’s heart-wrenching funeral was held Friday in the same Queens church where he was supposed to be the next day — as a groomsman in a wedding party for a best buddy.

A memorial to the fallen 31-year-old firefighter will now be placed in the church during the marriage service instead.

“The amazing thing about Timmy is that he accomplished so much in such a short time,” the Rev. William Sweeny said at Klein’s packed funeral at the Church of St. Francis de Sales in Belle Harbor, near where the dead fireman grew up.

“In fact, he was supposed to be in a wedding party tomorrow at a wedding of his dear friend’s that’s gonna be right here in this church. And they’re gonna set up a memorial in a very special way to thank Timmy for all the things that he did.”

Klein was set to be in the wedding party of close pal James O’Connor and his wife-to-be Danielle Mulle — and the couple has no plans to replace him, according to a friend.

“He’ll be remembered tomorrow and, for sure, celebrated,” Megan Ternlund, 31, said of Klein. “You can’t replace a person like that. He was best friends with Jimmy, the groom.”

She added, “He was going to be sitting at my table.”

The tragic revelation came as family and friends said a final goodbye to Klein — a deeply moving event that included his parents being given their late son’s fire helmet.

Also among the mourners were two smoke-eaters badly injured in Sunday’s fatal blaze — and who left their hospital rooms to attend the service.

One of the hurt firefighters, who was severely burned, rolled into the church in a wheelchair with his head wrapped in gauze to pay his respects.

The second one also left his burn unit to attend the heartfelt ceremony.

The firemen were set to return to the hospital after the service.

A third firefighter who suffered two broken arms in the blaze attended the funeral, too. He had been released from the hospital several days ago.

Klein, the son of a retired firefighter, was killed in the raging house fire in Canarsie in Brooklyn.

His mother, Dee Dee, gave a touching, sometimes funny eulogy, which revealed he’d suffered from “a rare form of anemia’’ as a baby. 

“We just had a special bond, as we spent a lot of hospital days and nights together,’’ she said.

“We believe going through his medical adversities played a very huge part in making him into the unbelievable human being he turned out to be,” the mom said.

She and her husband, retired firefighter Patrick, called their eldest child and only son “Sonny boy,” she said. 

The family of Steven Pollard – a late fellow hero Bravest and close friend of Timmy Klein’s who Klein had eulogized three years ago — also attended the funeral. Pollard died on duty in 2019 while helping at the scene of a Brooklyn car crash.

Firefighter Lyonel Rosemond, who worked with both men, said he was devastated to lose Klein so soon after Pollard. 

“First it was Steve, and now it’s Timmy. They were the good guys,” he told The Post through tears. 

“It’s like my boy, the person that lived through what I lived through when Steve passed, is gone,” Rosemond said of Klein, adding that the pair rode together in the back of an ambulance when Pollard was fatally injured.

Acting FDNY Commissioner Laura Kavanaugh choked back tears as she quoted the eulogy that Klein had given at Pollard’s funeral in 2019 —  using Klein’s own words to describe himself. 

“We lost a true hero that day,’’ she said, echoing the speech Klein gave about Pollard. “You will never be forgotten.’’ 

Klein also was remembered as a role model with a do-gooder streak.

“Maybe St. Peter’s house needs a ramp, and that’s why he was called” to Heaven, Sweeny told mourners, referring to Klein’s willingness to help those in need, including the disabled.

Mayor Eric Adams also offered his condolences to Klein’s loved ones during the service and praised them as the epitome of an “American family.

“You lost your son,” Adams said. “My heart goes out to you.

“Looking back, it was clear Tim was born to be a hero.”

Next to an altar, a framed head shot showed Klein grinning in his  uniform, surrounded by red flowers. His helmet was placed on a wooden pedestal nearby with  the number of his firehouse ladder, “170”, printed on it. 

Firefighters from Ladder 170 wore a purple patch with Klein’s name pressed onto their jacket sleeves in solidarity at the church, which is near Klein’s childhood home in Breezy Point.

After the service, firefighters carried Klein’s flag-wrapped coffin down the aisle as the song “Free and easy (Down the road I go)” by Dierks Bentley — one of the fallen hero’s favorites — rang through the church.

Before the funeral, bagpipers played “Amazing Grace” and police officers sat on mounted horses as mourners marched into the church. Outside, red ribbons were tied to trees and light poles in honor of the fallen hero.

Klein’s next-door neighbor, Tiffani Spinelli, said outside the Church of St. Francis de Sales in Belle Harbor, “He died just as he lived — a hero.”

“He was the best, most considerate, kind, and always worried about everyone else,” she said before the funeral.

Her son Mickey Spinelli, 12, said he admired Klein because he taught him hockey moves.

“Timmy was my hero. He taught me the techniques of the game. We used to play together,” the boy said.

The ceremony was flooded with supporters of the city’s Bravest, said Andrew Ansbro, president of the Uniformed Firefighters Association.

“It’s a horrible day, but it’s the feeling that, over the years, we have learned how to deal with,” he said. “We’re here to support the family. The turnout here reflects that. … This is a firefighters’ community and [people] lined the streets to pay their respects to our local hero.”

Earlier in the day, Commissioner Kavanagh said it “was an incredibly heartbreaking day for us, for the department, for the family.”

“Tim Klein is the 1,157th member to die in the line of duty. … It doesn’t make it any easier,” she said, describing him as “the best firefighter, the best son, the best brother, the kind of the guy that everyone relied on.”

A 21-year-old autistic man, identified as Carlos Richards – the son of a retired NYPD cop – also died in Sunday’s inferno.

“Our condolences go to the family of the firefighter who died trying to save Carlos,” a man told The Post earlier this week, after answering a number listed for Richards’ mother.

“Our hearts go out to his family. Right now, we’re grieving for Carlos, and we share the same pain that they are feeling,’’ added the man, who did not identify himself.

Additional reporting by Amanda Woods and Larry Celona