Johnny, 47, joined his Rango co-stars Isla Fisher and Abigail Breslin at the Four Seasons Hotel in Beverly Hills on Saturday for a press junket for their new animated flick.
And even teen pop star Justin, 16, who was staying at the same hotel, helped to promote the movie when he strolled in to the delight and shock of the audience.
The Canadian heartthrob told Depp: 'I'm a big fan of you so I want to support you.
'I just wanted to say hi.'
According to ETonline, Justin added: '[Depp] is a Belieber, and I’m a big fan of his.'
After the incident, the Pirates of the Caribbean star told the crowd: 'Who is not a Belieber now?'