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Amid Jimmy Fallon’s stunning loss in the ratings, Page Six hears that there’s turmoil at the top of the “Tonight Show” with one exec suddenly and mysteriously out and another tearing into boss Lorne Michaels as they struggle to fix the faltering show.

Fallon’s “Tonight Show” has been steadily falling behind newcomer Stephen Colbert’s “Late Show,” and on Wednesday it was revealed that Colbert has topped Fallon for a full season for the first time.

As Fallon’s famously fluffy show began to fall behind Colbert’s politically charged material, Fallon tried to ape Colbert by bringing in “Today” show vet Jim Bell as showrunner to inject some topical heat to the show.

But we’re told that — as the ratings continue to suffer in spite of that gambit — an anguished Bell is sniping at executive producer and NBC royalty Michaels, who heads up “Saturday Night Live” and a glut of NBC comedies.

30 Rock insiders say Bell is frustrated because he thinks that Michaels — who championed Fallon’s rise from “SNL” to his stint at “Late Night” and finally to “Tonight” — is “stuck in the past,” while Bell believes Fallon has to reinvent himself to compete.

A spokesperson for NBC told us, “We are really pleased with the innovation of ‘The Puerto Rico Show’ and ‘The Larry Sanders Show,’ under Jim’s leadership. We are excited for some new elements coming this summer and fall. Jimmy continues to share signature segments like slow jam the news, most recently with Presidential candidate Pete Buttigieg.”

Meanwhile, we’re told there’s a snarl because of an odd arrangement at the top of the ladder.

While Michaels is technically senior as the executive producer, Bell runs the show day-to-day as “executive in charge.”

In his seven-month reign, Bell has brought about changes, producing a number of outside-the-studio specials, even taking Fallon to Puerto Rico for a “Hamilton” special with Lin-Manuel Miranda.

Meanwhile, we’ve learned that Fallon’s longtime producer Katie Hockmeyer has now left — shortly after her return from maternity leave.

She started off as an NBC page before moving to “SNL” and working in Michaels’ office. She had been with Fallon since he launched “Late Night” in 2009.

A highly placed source told us that: “Katie no longer works at the ‘Tonight Show.’ She and Jimmy are still close — he adores her.”

“Katie is still an employee,” an NBC executive confirmed, while a source familiar with the situation said that “Katie has always been a valued leader in this company. She’s been with Jimmy for 10 years and is beloved by the staff.” It’s not clear what her new role at the network is.

Hockmeyer’s departure also comes just months after the “Tonight” show’s other longtime showrunner, Mike DiCenzo, quit.

DiCenzo cited burnout after 10 years on late-night TV and left as Bell — the executive producer of the “Today” show from 2005 until 2012 — took over.

The move mirrored one at insurgent CBS, in which executive producer Chris Licht moved from “CBS This Morning” to late night — with blockbuster results.

Bell has previously been the president of NBC Olympics Production and Programming.

Last year, Fallon admitted he sank into a depression following the intense backlash following his disastrous “hair ruffling” interview with then-candidate Donald Trump in 2016.

He said: “It was definitely a down time. And it’s tough for morale. There’s 300 people that work here, and so when people are talking that bad about you and ganging up on you, in a really gang mentality…”

Choking up, he continued: “You go, ‘All right, we get it. I heard you. You made me feel bad. So now what? Are you happy? I’m depressed. Do you want to push me more? What do you want me to do? You want me to kill myself? What would make you happy? Get over it.’ ”

Added Fallon: “I’m sorry. I don’t want to make anyone angry — I never do and I never will. It’s all in the fun of the show. I made a mistake. I’m sorry if I made anyone mad. And, looking back, I would do it differently.”

To all this, Trump then mocked Fallon on Twitter, writing: “Jimmy’s now whimpering to all that he did the famous ‘hair show’ with me (where he seriously messed up my hair), & that he would have now done it differently because it is said to have ‘humanized’ me-he is taking heat. He called & said ‘monster ratings.’ Be a man Jimmy!”

Fallon addressed the tweet on the show, saying, “First of all, I’ve never called this human in my life. I don’t have his number, I don’t want his number,” he continued. “And monster ratings? I’ve never said ‘monster ratings.’ I don’t know what he’s talking about.”

He also made a donation in the president’s name to the Refugee and Immigration Center for Education and Legal Services (RAICES).

Fallon has tried to incorporate more political humor into the show but has yet to match Colbert’s nonstop searing satire.