The 50-year-old actor purchased the piece which was created by street artist Bambi for his 10-year-old son and the image shows the 'Baby' hitmaker alongside the words "Rebel without a clue", reported Daily Star.
"Pax loves Justin and so Brad thought this would be the perfect gift for him. Brad loves Bambi's unique style and this is his third purchase from her. When he found out she'd done a piece with Justin, he knew he'd have to get it for Pax," a source said.
Apart from Pax, Pitt and his partner Angelina Jolie also raise Maddox, 12, Zahara, nine, Shiloh, seven, and twins Vivienne and Knox.