Jon Stewart made his return to "The Daily Show" on Monday night, except this time around, he was the one sitting on the other side of the famed desk.

According the Mashable, Jon Stewart's appearance was a tight-lipped secret - the guesting was under wraps up until the episode was taped. "The Daily Show with Trevor Noah" Twitter account only made the announcement on Monday morning.

"Tonight! A young man returns to call for congressional action on a 9/11 bill. #SeniorJonStewartCorrespondent," the tweet read, with an accompanying photo.

So what exactly happened? Mashable reports that the "monumental moment" was because of Jon Stewart's undying support for the Zadroga Act:

"It was what host Noah admitted as a monumental moment, but Stewart did not find himself back at the iconic desk for just any reason - he was there to show his support for the Zadroga Act, which provides compensation and medical funds to 9/11 first responders."

Technically, the Zadroga Act had already expired. But Jon Stewart, along with activist groups, are gearing up in an attempt to "get the bill renewed before Congress goes out of session later this week in order to secure funds."

As it turns out, Jon Stewart had been supportive of the cause for several years now. It was in 2010 when Jon Stewart recruited a panel of first responders to share their experiences - hoping to get more supporters for the bill, which President Barack Obama signed into law back in early 2011.

During his return, Jon Stewart also brought back one of the first four panelists from five and a half years ago - Kenny Specht.

Specht was the founder of the New York City Firefighter Brotherhood Foundation, and while on the show, Kenny explained that two of the other original panelists have fallen ill and could not disclose the details.

The other empty chair was supposedly for John Devlin, who had already passed away. "When we did the show five-and-a-half years ago, four men sat here. [Now] it's just you and I," Kenny Specht told Stewart.

Watch out for an update - video segments will be posted once they are available.