While Hollywood debates the merits of “Green Book” as this year’s best picture Oscar winner, the rest of America is still discussing Sunday night’s showstopping number from Lady Gaga and Bradley Cooper. The “A Star Is Born” duo performed “Shallow” midway through the Academy Awards, and it was one of the night’s most buzzed-about highlights.

For the Oscar producers, it was also an opportunity to do something a bit different. Rather than have someone introduce the performance, the first few notes of the song — instantly identifiable to most, given its popularity and use in “A Star Is Born’s” marketing campaign — began playing. Cooper and Gaga, sitting in the front row of the Dolby Theatre, locked hands and walked on stage.

“Nobody knew where it was going to be in the show,” Rob Mills, ABC’s senior VP of alternative series, specials, and late-night programming, told Variety. “And the fact that it came right out of a speech gave it that element of surprise. Normally, if you’re in the house, you’re going to see that Bradley and Lady Gaga aren’t in their seat. The fact they actually went from their seats to the stage up there, that surprise was so great. Obviously, the song is engineered to be one that kind of crescendos to that kind of energy. It was just electric in the house.”

As he celebrated the show’s ratings bump — up by 3.1 million viewers and 13% among adults 18-49 from last year — Mills spoke with Variety on Monday afternoon for a dive into the deep end of this year’s host-less Oscars, including the cold Queen + Adam Lambert open, Melissa McCarthy’s and Brian Tyree Henry’s elaborate costumes, and that memorable moment in the “Shallow.” Some highlights:

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Bradley Cooper, as well as Lady Gaga, staged their “Shallow” performance themselves, working with Oscars director Glenn Weiss

“Bradley and Gaga, they really had this idea in their head of how they wanted it to be,” Mills said. “And the producers really worked step-by-step with them to make that what they were envisioning a reality… this was staying true to the spirit of the movie as well. They really wanted to kind of embody everything that the characters in the movie stood for in this three-minute number.”

Mills said it helped that Weiss was also an executive producer on this year’s Oscars, which made it easy to “meticulously work with Bradley on every element. They would walk through the whole thing and how it’s going to look and go. They really rehearsed the hell out of it, and they made it so it was just seamless. Even in rehearsal you knew, this was one of those things that’s going to be played in those montages of all-time Oscar moments.”

It also didn’t hurt that Cooper, as the director of “A Star Is Born,” and Gaga, who’s no stranger to concert staging, had the chops to do more than just show up and sing.

“That was the thing, he was able to work with Glenn and knew what he wanted to see, what the look he wanted to be,” Mills said. “That always goes a long way. And Gaga too. She has a big hand in how she stages her shows.”

Cooper, Gaga, and Weiss had been working on the number since “Shallow” first received its nomination in January, but it all came together during rehearsals over the weekend. Everything was meticulously planned out and choreographed, from the idea of facing the camera outward (with the audience behind the singers), to Cooper moving his microphone stand before sitting down next to Gaga at the piano.

Mills said it was no surprise that Cooper and Gaga got a standing ovation at the end of their number, and again when they returned to their seats from backstage. And yes, he noticed their chemistry too.

“It was definitely something you could feel in the house. It came through on the screen, it was everywhere,” he said. “There was real heat there.”

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Maya Rudolph, Amy Poehler, and Tina Fey were given carte blanche to do as much as they wanted with the open.

No host, no problem. The “SNL” alums all have plenty of hosting experience, and were the easy choice to line up first as presenters once it was clear there would be no Oscar host this year.

“The offer was do as much or as little as you’d like to do,” Mills said. “If they had said they wanted to host nobody would have said no. Whatever they wanted to, they were always welcome. We always knew that first award was going to be somebody who doubled as a sort of host, and could give a quick two-minute comedic monologue.”

“When you don’t have a host you can give the presenters more time,” he added. “So if they’re funny and they want to use it, that’s great. That was a no-brainer. And they rose to the task of at the very least opening the show the same way you would with a great host like a Jimmy [Kimmel].”

Queen’s open might have been “Bohemian Rhapsody,” but that idea was shelved due to time constraints

“Bohemian Rhapsody” is not a short song. That’s part of the reason why Queen and Adam Lambert ultimately went with the one-two punch of “We Will Rock You” and “We Are the Champions.”

“‘Bohemian Rhapsody’ was talked about because that’s a roller coaster of a number,” Mills said. “But at the end of the day, those two songs really had the right energy and you were able to get you right into the show.”

The idea of Queen opening the show was inspired by the energy in 2017 when Justin Timberlake opened the ceremony.

“You rarely get an opportunity to organically include some music,” Mills said. “Queen had just made sense because of the movie. It was great to be able to use a rocker to open the show. It wasn’t the normal, stately opening that you normally see.”

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Melissa McCarthy came up with the idea for her and Brian Tyree Henry to come out dressed in wild costumes

In presenting the Oscar for outstanding costumes, the duo paid tribute to the nominees: McCarthy wore a dress inspired by “Mary, Queen of Scots,” and was covered with stuffed rabbits as an homage to “The Favourite.” Henry, meanwhile, wore an outfit inspired by “Mary Poppins Returns,” “Black Panther,” and “Mary, Queen of Scots.”

Mills said McCarthy came up with the idea after this year’s presenters were told that, without a host, they could “go crazy if you have an idea.”

“Melissa, this was completely her idea,” Mills said. “And nobody is better at doing a straight read while being in that ridiculous costume with those stuffed animals than Melissa. Brian completely went along for the ride. It was fantastic. That to me was a great Oscar moment.”

Besides Queen, Kendrick Lamar might have kicked off the Oscars

But ultimately, Lamar wasn’t able to make it to the show at all, which is why (as previously reported) he and SZA weren’t there to perform “All the Stars.”

“There was talk at some point that maybe it would open the show,” Mills said. “It does sound like when Kendrick is in writing and recording mode it’s hard to get out of that.”

Where’s Whoopi?

The hashtag #WheresWhoopi popped up on social media Sunday night, as some conspiracy theorists had convinced themselves that Whoopi Goldberg might show up as the Oscars’ surprise host. But Goldberg, who had previously been announced as a presenter, didn’t show up at all.

But Goldberg also hasn’t been seen on “The View” in recent days due to illness.

“She really was sick,” said Mills, who added that they wouldn’t have kept the news of an actual host secret. “Keeping things a secret doesn’t do anyone any good, trust me. If she was the host, we would have shouted it from the mountain tops.”

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Not much was cut from the show this year, as the show had already been trimmed down to a sleek, three hour-ish run time

“This thing was cut to the bone,” Mills said. “As you saw, the only montage we had was at the beginning, and that was only 90 seconds. Everything ran according to plan. Once we got to the dress rehearsal, it became the most relaxed Oscars in years. You knew there wasn’t going to be a lot of politics, you knew how the show was going to run. For us, we knew all the beats on the show and the speeches were the only unpredictable part. It was actually kind of nice.”

Despite the high marks for the anchor-less telecast, there’s still a good possibility that a host will return next year.

“I think what you’ve learned is you don’t need to have a host just to have a host,” Mills said. “You see it works when it’s host-less, but you can’t forget how great Jimmy Kimmel did, how great Billy Crystal did, how great Johnny Carson and Bob Hope were all these years.

“Imagine, what would have happened if the whole envelopegate had happened this year and we didn’t have a host?” he added. “It’s hard to imagine that moment now without Jimmy, who was able to rein in the chaos and make light of what was a crazy situation. I think like everything, you look at what worked and what could have been better. I certainly think a host will be in the conversation for next year — but it doesn’t mean that you have to have it.”