Brad Pitt bruised his face falling over in flip-flops.

The 'Tree of Life' actor stepped out at the Light Up the Blues Concert in Hollywood for Autism on Saturday (25.04.15) with a huge mark across his face, and it has now emerged he sustained the injury after taking a late-night tumble in unsupportive footwear.

His spokesperson said: ''This is what happens when you try to run up steps in the dark, with your arms full, wearing flip flops. Turns out if you then try to stop your forward momentum with your face, the result is road rash.

''Regardless, I wasn't going to miss the Autism Speaks benefit the night after - wonderful people and I was honoured to be a part of this important event.''

During the evening, Brad - who raises children Maddox, 13, Pax, 11, Zahara, 10, Shiloh, eight, and six-year-old twins Knox and Vivienne with wife Angelina Jolie - won a bidding war to take home a guitar signed by all the event's performers.

He paid $23,000 for the instrument.

Other celebrities in attendance at the concert - where all the performers were autistic - at the Pantages Theatre included Christina Applegate, Gary Cole and Amy Brenneman, while Jack Black was the evening's host.