FOUR of NBC News’ biggest stars have been dragged into an ugly sex scandal as the network kicks off its coverage of the 2014 Winter Olympics, although all have issued denials.

The ENQUIRER has learned “Today” show co-host Matt Lauer and weather­man Al Roker, along with “NBC Nightly News” anchor Brian Williams and sportscaster Bob Costas – all of them married – are at the center of Internet speculation in reported extramarital hijinks!

The scandal erupted when the “New York Daily News” reported on Jan. 28 that “a secret, steamy relationship between one of NBC’s best-known on-air personalities and a network staffer has been put on ice because the duo fear their naughty behavior will be exposed by eavesdropping Russian agents at the Olympics” in Sochi.

Neither the gender nor the names of the cheaters was identified. But the newspaper claimed the staffer admitted “to a 20-year-long, on-and-off again shagfest turned sexting bonanza,” and is frustrated the hanky-panky “will be on hiatus as long as one of them…is covering the Games.”

The blockbuster report sparked an online “guessing game” as to who was involved – and bloggers jumped on the juicy fact that the on-air star had been at NBC for at least 20 years.

Speculation focused on 33-year NBC veteran Costas; Lauer, who joined the network in 1992; Williams, who has 21 years with NBC News under his belt; and Roker, who has been with the network for 30 years.

Lauer and Williams quickly denied any involvement, and Roker strongly denied the story> Costas reportedly called the news­paper directly to say he was not involved. Most specula­tion centered on Lauer, a 56-year-old father of three with a long history of cheating scandals.

Just two years after their 1998 wedding, Lauer’s wife Annette Roque learned that he carried on an affair with married 26-year-old Jessica Thorman while they were engaged. In 2006, a pregnant Annette filed for divorce amid rumors that Lauer had been involved with “Today” colleague Natalie Morales while covering the Winter Olympics in Torino, Italy. Annette later withdrew the petition.

And in July 2013, sources told The ENQUIRER that Lauer was “obsessed” with a 20-year-old college coed who was appearing on the show, although the young woman’s father said that Lauer’s dealings with his daughter were “professional and appropriate.”

A New York network TV insider added: “This couldn’t come at a worst time for NBC, and if the cheater is at the ‘Today’ show, there will be hell to pay. The show’s ratings took a hit when Ann Curry was forced off the set, and Lauer appeared to be the top bully. If he’s the guilty party, viewers – not to mention his wife – will have had enough.”