AceShowbiz -

Hilary Duff apparently finds everything about his baby boy interesting. The 24-year-old actress, who played Olivia Burke on several episodes of "Gossip Girl", recently opened up to PEOPLE about Luca's biggest milestone to date, and went on to reveal where she's keeping her son's belly button.

"You know what was a big milestone? The belly button falling off," she gushed. "That was a huge one. And then I wanted to keep it but my husband was like, 'No, that's gross, you can't keep it!' I'm like, 'I'm totally keeping it,' and I secretly kept it. But now it's not a secret anymore. It's in a Ziploc bag in the back of my makeup drawer. Luca's going to think I'm a freak!"

The new spokesperson for Johnson's Baby Cares initiative also claimed she enjoyed nursing her 4-week-old son. Describing it "such a wonderful bonding time," the leading lady of "The Lizzie McGuire Movie" elaborated, "Just to have your baby thrive and knowing that you're doing that and you're responsible - it's such a rewarding feeling."

Duff gave birth to her first child with husband Mike Comrie on March 20. She broke the news herself two days later by tweeting, "Welcome to the World Luca Cruz Comrie! Tuesday evening, we became proud parents of a healthy 7 pound 6 ounce beautiful boy." Around two weeks later, she shared photos of her little boy being wrapped in a muslin swaddling blanket.