Bradley Cooper cries over Robert De Niro 'Inside the Actors Studio' clip

Bradley Cooper is the star of this week's psychological thriller, "Limitless," but it wasn't so long ago that he was in the audience of "Inside the Actors Studio," asking his co-star Robert De Niro questions.

On Monday's "Inside the Actors Studio" host James Lipton played a video of Cooper's first interaction with De Niro which brought the "Hangover" actor to tears, in the clip, Cooper asked De Niro about what inspired his "Awakenings" character and the screen legend essentially brushed him off.

"I'm a loud crier," Cooper told the "Actors Studio" audience. "I'm not like a sobber... I'm like a -it's ugly, so I apologize."

Cooper recently expressed his appreciation for De Niro at the premiere of "Limitless," which hits theaters on Friday.

"The best thing about him is how willing he is to share all of that knowledge and experience," Cooper told OnTheRedCarpet.com of De Niro. "He's just another actor on the set with you and he's so real. It was the easiest time I ever had acting. Ever." In "Limitless," which hits theaters on Friday, March 18, Cooper plays Eddie Morra, whose life is changed after he takes the to-secret drug NZT, which gives him superhuman abilities.

Cooper did an interview with ABC News Now's "Popcorn With Peter Travers and talked about how he was originally afraid to appear on Lipton's show because he didn't feel like he had earned the right yet.

"I didn't want to do it," Cooper told Peter Travers. "[Lipton] asked me to it a year ago. I thought I'd feel like a fraud up there. The blue cards would be this thick [Cooper pressed his thumb and pointer finger together], the interview would last 10 minutes and it would be over. Then I thought, the whole point of this show is to talk with the students. Of course I'll do it. And I'm really glad I did it after this movie."

Cooper holds the honor of being the first graduate of the Actors Studio Drama School to be invited on the show.

The actor's girlfriend of two years, Renee Zellweger was also in the audience of "Inside the Actors Studio." The couple has remained quiet on details of their relationship.

At the premiere, Cooper also dispelled the rumor that Charlie Sheen would make a cameo in "The Hangover Part 2," which is set for release on May 26.

Watch the trailer for "Limitless" below.