EXCLUSIVE: Penelope Cruz & Javier Bardem Double Date With Sean Penn & Mystery Brunette

Undercover couple Javier Bardem and Penelope Cruz tried to have a quiet drink with Sean Penn and a mystery brunette Friday night, but the boys got so raucous everybody in the room knew they were there -- including RadarOnline.com!

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The trio of Oscar winners sat at a secluded table on the outside patio at the Four Seasons Hotel Los Angeles with Penn's date listening to their animated stories.

Penelope, who recently refused to reveal to David Letterman if she is engaged to handsome Bardem, sat with her back to the bar crowd in an attempt not to be recognized. But her low profile ploy was blown by Bardem and Penn who were laughing loudly at each other's jokes. At one point Penelope even had to gently calm handsome Bardem down by holding his arm as he enthusiastically got out of his seat waving his hands.

"Everyone seemed to be having a good time except Penn's date who appeared slightly subdued," our eyewitness said.

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Cruz and Bardem first met after working on Jamon Jamon together in 1992. Their romance took off after they appeared on the big screen again in 2008's Vicky Christina Barcelona.

Penn is currently single after splitting with the mother of his two sons, actress Robyn Wright Penn.

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Cruz sparked engagement rumours after she was spotted wearing a sapphire and diamond sparkler on her ring finger at the October premiere of Broken Embraces. But when asked by Letterman to confirm, the 35-year-old star said, “I don’t feel comfortable talking about my private life in public."