The TMZ Hollywood Tour -- the only way to see huge celebrities ... and a well-dressed speed metal fan working up the nerve to ask his gf to marry him. Yeah, that really happened ...  

Check out TMZ on TV -- click here to see your local listings!

The maiden voyage of the TMZ Hollywood Tour set sail today and right off the bat they caught a BIG ONE ... spotting Diddy roaming the streets of Beverly Hills!


It went down on Rodeo Drive just minutes ago. The bus tour was cruising along ... when they saw Diddy out shopping. So our fearless leader, Harvey Levin, jumped out of the bus and ran to catch up with him. 

Turns out Diddy isn't just a fan of Harvey's work on TMZ ... he's a fan of his singing, too! Ok, he didn't actually hear HL's "My Way," .... he heard about it. But still!

To get your tickets for the TMZ Hollywood Tour, click here -- you never know who you're gonna see!