Watching “Michael Jackson’s This Is It” will have fans grieving once again, but this time, it won’t only be for the fallen King of Pop, but for what we lost — a brilliant entertainer who gave every inch of his body and soul for what might have been one of the most spectacular comebacks of all time.

Jackson never got to complete that comeback, dying days before his London concerts were to begin in July, but “This Is It,” culled from hundreds of hours of rehearsal footage for those shows, does it for him. Even though it’s been well edited, the amazing performances Jackson delivers in this film are not a result of camera magic, but Jackson’s own.

When Jackson announced his “This Is It” concerts earlier this year, many wondered whether Jackson had any magic left at all. Besides his tattered reputation, he was rumored to be in frail health and hadn’t performed a major concert in almost a decade. There were well-deserved skepticism about whether Jackson had the vocal and physical agility to stage the kind of concerts that wowed fans in his prime two decades earlier.

“This is It” gives both answers an emphatic yes. Even though Jackson’s looks — with his weirdly delicate face and his stick-thin frame — still makes one squirm with discomfort, once he starts to perform, that discomfort gives way to amazement. At 50, Jackson was still an amazingly gifted dancer with moves that leave your mouth agape. Though we only see him do the moonwalk once, and just fleetingly, his stop-on-a-dime spins, deft footwork and body jerks recall the Jackson the world fell in love with 25 years earlier with “Thriller.” And Jackson’s voice still dazzles — even when he’s trying to play it down.

“I’m trying to conserve my voice,” Jackson says at one point — then delivers a vocal that is spine-tingling — and these are just run-throughs, not the actual show.

Fans never get to see what would have been the “This Is It” concert — full dress rehearsals weren’t due to happen until the show went overseas for final rehearsals. Instead, the movie takes from segments of taped rehearsals, and also weaves in film segments Jackson planned for the concert to give at the very least an idea of how the concert might have looked.

A graveyard scene meant to be in 3D was planned for Jackson’s performance of “Thriller,” and a computer-animated dancing army would have accompanied Jackson on screen for a militaristic version “They Don’t Care About Us.” Jackson kept much of the same moves from his classic “They Way You Make Me Feel” video — including the floor humping — as well as the

groundbreaking choreography from his “Beat It” clip.

But whether it was through new visuals and different musical arrangements, he appeared to be breathing new life into his well-worn catalog, promising fans a show that would have taken Jackson and his fans to new heights. Jackson is gentle but authoritative as he demands perfection from his crew, whether it’s gently taking the audio crew to task for making his earpiece too loud or attempting to elicit a grand performance from his young star guitarist.

“This is your time to shine,” he says in that famously soft soprano voice before delivering a high wail and challenging her to do the same on her guitar.

The film doesn’t give viewers much insight into Jackson outside of performance mode — we only see him rehearsing or hear him talking about music, or the meaning of his songs. Yet the film does give a glimpses into Jackson’s personality — alternatively playful and shy, firm yet understanding, often saying phrases like “with love” after giving a command.

The film also splices together different performances of the same song at times, leaving one to wonder why. Is it for a visual effect? Or did he not complete enough in one take?

Thankfully, there appears to be enough full takes so one’s mind does not play into conspiracy theories. There were certainly critics of “This Is It” before its release — those who wondered whether it would be an exploitative flick, a quick attempt to cash in on his newfound popularity, and those who felt the preparations for the concert contributed to his death.

But “This Is It” is a beautifully made, loving tribute that gives Michael Jackson what he so desperately wanted — affirmation that he indeed was the greatest entertainer of our time.

“Michael Jackson’s This Is It,” released by Columbia Pictures, is rated PG for some suggestive choreography and scary images. Running time: 111 minutes. Three and a half stars out of four.