New Calvin Klein model Justin Bieber never wears his designer underwear more than once, and throws each pair away when he's finished with them.

The pop superstar became the latest celebrity to take part in a 'carpool karaoke' skit with British comedian James Corden on his The Late Late Show on Wednesday (20May15), during which the odd couple sang along to Bieber's hits Baby and Boyfriend and Boyz II Men's End of the Road, changed clothes and chatted.

During his pre-taped in-car interview, the pop pin-up confessed he is sent so much underwear from the company, he never has to wear the same pair of briefs twice, explaining, "(I have) boxes and boxes... There's so many."