TMZ Live Gladys Knight Calls In Harvey & Charles SING BACK-UP

2/21/2012 12:30 PM PST

TMZ Live: Gladys Knight Calls In ... Harvey & Charles SING BACK-UP

What's the greatest Motown song of all time -- tough question ... but we got one of the greatest experts ever to weigh-in ... Gladys Knight.

She's also got two new Pips -- Harvey and Charles sing back-up ... or at least they try. And if that wasn't enough -- Stevie Wonder also calls in and gives us his picks.

Also, are Rihanna and Chris Brown pulling the most irresponsible publicity stunt ever?

(2:00) Harvey is BEYOND excited! One of his all-time favorite singers -- Motown legend Gladys Knight -- is on the phone!
(3:15) Gladys explains the magic of Hitsville USA -- and how music wasn't the same after Motown moved to L.A.
(4:30) Gladys tells a story about Hitsville that she's NEVER told before.
(8:10) Gladys reveals her favorite songs to sing ... and her favorite hits by the other Motown greats.
(14:45) Gladys sings "Midnight Train" ... and Harvey and Charles sing backup!!! Classic.
(17:30) Rihanna and Chris Brown collaborate on two songs together -- most people in the newsroom are disgusted by it.
(34:50) Stevie Wonder is on the phone! Harvey and Charles can't believe it ... and think we're screwing with them.
(37:01) Stevie's turn to reveal his favorite Motown hits.
(40:00) Stevie talks about being a kid at Hitsville -- and how Marvin Gaye showed him how to hold drum sticks.