Simon Cowell 'at the heart' of NBC's 'America's Got Talent' investigation about Gabrielle Union

Simon Cowell is said to be in the crosshairs as NBC launches a formal investigation into the alleged toxic culture on "America's Got Talent."

The investigation is well underway, with the network having already met and discussed formalities with Gabrielle Union. The actress shared that she met with the executives for a "lengthy 5-hour" yet productive meeting on Tuesday, where she shared nothing but the "unfiltered truth."

An NBC spokesperson told Deadline that initial conversations with the actress have been "candid and productive." The representative added that the network is looking forward to having more discussions with Union in order "to come to a positive resolution."

The discussion with Union is only part of the investigation as an insider revealed that Cowell is at the heart of it all. NBC has yet to talk to him about the alleged toxic culture on the show and has yet to discuss how things should be done moving forward.

The source claimed that the discussion with Union revolved in great part about Cowell's "behaviour and overlording of the Fremantle and Cowell's Syco produced AGT." The Brit, who is a judge and creator of "America's Got Talent," has the final say on what should and should not be done on the competition series.

"The ball is in NBC's court to see if they can get Cowell to agree to make some changes to the way things are done on the show," the source told the publication.

Late in November, fans of the show were shocked to hear about Union and Julianne Hough's departure from "America's Got Talent." While Hough said she enjoyed her time on the show, the "Bad Boys" star experienced otherwise. She spoke up against "racist incidents" involving Jay Leno and reportedly complained about Cowell smoking illegally inside his dressing room.

Prior to Union getting fired from "AGT," she and Cowell reportedly had a meeting at his Malibu home, from which NBC gathered the details during their long discussion.

Following Union and Hough's departure, former "America's Got Talent" judges Sharon Osbourne and Howard Stern called Union's ousting as Cowell's orchestration. Osbourne even called the show a "boy's club."