11/10/2008 AT 01:25 PM EST
Proud grandfather Lionel Richie has some sage words for daughter Nicole Richie
: Not only will her own daughter grow up fast, she'll soon be moving fast, too.
"I call her 'The Mouse'," Richie said of his 10-month-old granddaughter, Harlow, "and The Mouse holds on to the edge of a chair now and is gaining the confidence to think, 'Maybe these legs belong to me.' I keep telling Nicole that it's a bad sign, because once those legs gain confidence, then they're out of here!"
Richie, whose new album, Just Go
, hits stores next month, tells PEOPLE he continues to be amazed not only by Harlow's growth, but that of his one-time wild-child, Nicole, who's transformed into a devoted mom with boyfriend Joel Madden.
"I'll be visiting the house," Richie says with a laugh, "and Nicole will be like, 'Dad, lower your voice! Harlow is sleeping!'
"We must be talking about someone other than my daughter! This is not the same Nicole that brings 15 friends over to my house while [Lionel's daughters] Myles and Sofia are sleeping, and says, 'Dad, what's the problem?' "
Adds the elder Richie, "This is whole new territory, and I couldn't be happier."
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