Lionel Richie's grandchildren didn't know he's famous!

Lionel Richie has revealed that his two grandchildren had no idea about he was a superstar until recently.

The 'Dancing on the Ceiling' singer explained that his granddaughter Harlow, 4, and 2-year-old grandson Sparrow had never seen their grandfather on stage until he duetted with their father Joel Madden on Australian TV on Sunday.

'While we were singing, I could see [daughter] Nicole with Harlow and Sparrow out of the corner of my eye, and it dawned on me they have never seen me on stage before,' explained Lionel to Courier-Mail.'

'You just know they were thinking, "What's Pop-pops doing with Dada?"'

Richie and Madden performed a rendition of 'Easy', one of Richie's biggest hits with his former band Commodores, and Lionel admits he would have been nervous had the tables been turned.

'Singing with your father-in-law is enough to make you nervous,' joked the 62-year-old. 'I would have passed out.

'It could go all wrong. But it was great.'

Lionel Richie and Friends in Concert