Robert De Niro breaks down in tears as he discusses the plight of bipolar illness portrayed in Silver Linings Playbook

Robert De Niro wasn't acting when he broke down in sobs on Katie Couric's day time talk show Monday.
The usually tough-guy actor was a guest on Katie to discuss the hit film Silver Linings Playbook with director David O. Russell and co-star Bradley Cooper.

When asked about the film's premise - that of a bipolar character trying in vain to fit in - The Goodfellas actor began to cry.
Scroll down for video...

Still emotional: Robert De Niro teared up while talking to Katie Monday about playing the father of a son who suffers from bipolar disorder in Silver Linings Playbook

Father and son: Bradley Cooper plays Pat, who suffers from bipolar disorder. As with most mental illness, the family suffers as much as the afflicted person

'Did you feel a greater responsibility about doing a film that David had so much personally invested in?' the anchor asked, following up on a question asked of Russell.
'Of course, I uhm – I understand,' replied De Niro, who plays the father of Bradley Cooper's troubled Pat. After a long pause, he tried to continue, but sobbed up.
'I don’t like to get emotional, but I know exactly what he goes through.'

Rare display: The Godfather actor is usually very reserved during interviews

Top journalist: Katie Couric is known for drawing out her guests

Russell was inspired to write the film because his son suffers from bipolar disorder as well as Obsessive Compulsive Disorder.  Those are the mental illnesses that plague Cooper’s character Pat.
'There’s nothing harder in life than when you can’t, can’t figure out what to do,' Russell said about dealing with a character like Pat. 'You try everything, and you must never stop. Your heart just has to keep growing.'

Personal experience: Director David Russell, right, was inspired to write the film because his own son suffers from bipolar disorder

Lighter moment: Bradley Cooper cracked up while talking about his career in movies such as Wedding Crashers and The Hangover 

Silver Linings Playbook has been the surprising hit of the year and has been nominated in virtually all award competitions.
Jennifer Lawrence, who plays Pat's equally troubled girlfriend, already won the Golden Globe for Best Actress and most recently she won the same category at the Screen Actors Guild Awards.

 VIDEO  Robert De Niro breaks down in tears on TV chat show... 

You talkin' to me: The Taxi Driver star looked peeved with Bradley in this scene from the hit film

phgh