Sandra Bullock declared her enviably taut derrière a 'hairy mess' on Thursday's episode of The Ellen DeGeneres Show.

The 51-year-old Oscar winner was discussing a scene where she mooned co-star Billy Bob Thorton from a bus window in their film, Our Brand Is Crisis.

'I'm freakishly modest which - I know it doesn't come across that way - but I am,' admitted the Heat funnywoman, who plays a retired political consultant called 'Calamity' Jane Bodine.

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Modest as always: Sandra Bullock declared her enviably taut derrière a 'hairy mess' on Thursday's episode of The Ellen DeGeneres Show

'And for some reason that day, I think because it was so hot, we were in some airplane hanger [and] the bus wasn't moving. There was just green screen, and I was dropping trou and hanging it out the window. Not even thinking who's on the other side to see that mess!

'And the side view, in the coming back in, trying to get your butt off the ledge and get your pants back up and you notice the thong came down with it sometimes.'

At first, Sandra tried to pretend her co-star Anthony Mackie - who plays Ben - was her butt double for the David Gordon Green dramedy.

'I was dropping trou and hanging it out the window!' The 51-year-old Oscar winner was discussing a scene where she mooned co-star Billy Bob Thorton (L) from a bus window in their film, Our Brand Is Crisis

'Well he's got an incredibly soft bum!' At first, Sandra tried to pretend her co-star Anthony Mackie (L) - who plays Ben - was her butt double for the David Gordon Green dramedy

No Tinder for Sandy! During a round of Never Have I Ever, all the Our Brand Is Crisis castmates admitted to never having tried online dating and lying to police

'Don't bring that up!' The single mother-of-one was forced to defend herself when everyone else revealed they hooked up with someone in the back of a limousine

'Well he's got an incredibly soft bum,' Bullock joked.

'Anthony's butt is so smooth. How does that happen? I said, "I'm sure people would rather see me with a smoother butt than with the hair that I've got growing down there."'

During a round of Never Have I Ever, all the Our Brand Is Crisis castmates admitted to never having tried online dating and lying to police.

She plays a retired political consultant: The Gravity actress reunited with her co-star George Clooney to co-executive produce the film, which centers on an American-style campaign in a Bolivian election

Halloween opening: Our Brand Is Crisis, based on Rachel Boynton's 2005 documentary, hits US theaters Friday and UK theaters January 22

The single mother-of-one was forced to defend herself when everyone else revealed they hooked up with someone in the back of a limousine.

'What about prom? What did you do at prom?!' Anthony challenged.

Sandy frowned and replied: 'I came home early because we broke up two weeks before! Don't bring that up!'

The Gravity actress reunited with her co-star George Clooney to co-executive produce the film, which centers on an American-style campaign in a Bolivian election.

'Usually I wear whatever my son asks me to wear': This weekend, the Golden Globe winner will go trick-or-treating with her adopted son Louis, who chose a Teenage Mutant Ninja Turtle costume (pictured in 2014)

Bullock told Access Hollywood this week: 'Out of all the choices he picked out the sluttiest Batgirl. I said, "Momma doesn't feel good (about this)!"'

Bullock continued: 'I don't mind the slutty Batgirl, just not around kindergarteners!' (pictured in 2013)

Our Brand Is Crisis, based on Rachel Boynton's 2005 documentary, hits US theaters Friday and UK theaters January 22.

This weekend, the Golden Globe winner will go trick-or-treating with her adopted son Louis, who chose a Teenage Mutant Ninja Turtle costume.

'Usually I wear whatever my son asks me to wear; it's usually in combination with his,' Bullock told Access Hollywood this week.