The pair rocked it out together in Seventies band Faces before both going on to bigger and better things. But the Rolling Stones guitarist wants Rod by his side when he says 'I do' to theatre producer fiancée, Sally Humphreys.
'Ronnie might be nervous when Rod makes the speech,' a source told Britain's Mirror newspaper. 'They have been in a lot of scrapes over the years so he will have a lot of stories to tell!'
Rod, 67, and Ronnie, 65, have been friends for nearly 50 years but the best man duties will be shared with Rolling Stone Keith Richards and one of the groom's three sons.
Ronnie popped the question to his 34-year-old bride-to-be after dating for just six months but the pair have been friends for over 10 years. 'Ronnie is absolutely besotted with Sally and they have a lot in common,' the insider added.