As soon as he found his footing on “Late Night,” Jimmy Fallon’s promotion to the “The Tonight Show” desk was taken as a given within NBC. The announcement of the Jay Leno-Fallon handoff, set for February following NBC’s coverage of the winter Olympics, was hastened by ABC’s recent move of “Jimmy Kimmel Live” to the 11:35 p.m. slot — but not by much, according to Peacock insiders.

(From the pages of the April 9 issue of Variety.)

Fallon was the natural choice to succeed Leno, and not just because of his apprenticeship in the 12:35 a.m. hour. NBCUniversal brass see him as the host with the strongest potential to have the mainstream appeal that has kept Leno No. 1 in latenight for more than 20 years.

The celeb impersonations, skits and song parodies that have become Fallon’s energetic trademark, honed during his six years on “Saturday Night Live,” are hardly toohip-for-the-room material. But by virtue of his age, 38, he’ll bring a generational shift in tone and content to “Tonight Show.”

Fallon has gained street cred with latenight’s target demo through his embrace of social media and knack for delivering viral videos that keep auds chattering. “The Evolution of Mom Dancing” (pictured above), featuring Fallon’s fancy footwork with Michelle Obama, has logged nearly 15.5 million views on YouTube alone since it was uploaded Feb. 22:

“He’s just magic in front of an audience,” said Lorne Michaels, who ushered Fallon into the “Late Night” host slot in 2009 and will continue as his exec producer when “Tonight” relocates to Gotham next year.

“Part of the appeal of those pieces is that they go viral and reach a whole other audience,” Michaels said. “Jimmy tweets during the taping. He’s so strongly connected to his audience and so much of the audience now watches it online.”

NBC took a beating in the public eye during the past few weeks as rumors of the “Tonight” transition spread, with many perplexed at why the Peacock was so eager to shake up a show that has long been No. 1 in its timeslot.

But NBC brass had already determined that the two-year pact Leno reached with the network in 2012 would be his last on the show. The goal was to finesse the installation of Fallon while “Tonight” was still on top.

As reports of the Fallon rumors spread, NBCUniversal CEO Steve Burke was determined to avoid, as much as possible, a replay of the 2009 debacle with Conan O’Brien, whose eight-month tenure at “Tonight” was complicated by the network’s decision to install Leno in a 10 p.m. nightly show.

Burke flew to Los Angeles on March 24 to huddle with Leno — the first time the two had met since Burke took over NBCU in late 2010 — and discuss scenarios that allow him a graceful exit from the desk he has manned since succeeding Johnny Carson in 1992. Leno was suitably impressed by the outreach from the Peacock’s big boss.

After the formal Fallon announcement was made April 3, everyone at NBC, from Burke on down, fell all over themselves praising Leno’s “graciousness” in the succession process.

As the dust settles, hopes at NBC are high that Fallon will be a demo-friendly worthy successor, and that Leno’s benevolence to the institution he’s about to hand over will keep him from mounting a rival latenight program any time soon.