"Diana Ross just walks in," Evan Ross recalls of his mom being in the delivery room when daughter Jagger Snow, 3 next month, was born

For Evan and Ashlee Simpson Ross, the day their daughter was born is one they won’t be forgetting anytime soon — for more reasons than one.

The spouses spoke to PEOPLE Thursday at the launch of their unisex Zadig & Voltaire line (called Jagger Snow, after their 2½-year-old daughter) in West Hollywood, California, where they recounted the hilarious events surrounding their little girl’s July 2015 birth.

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“Probably our parents coming in before it was time to come,” Ross, 29, says of the most memorable moment from the day. “I was like, ‘What are y’all doing?!’ ”

“While [Ashlee] was having the baby, we said we were going to do it just us, but then we saw both our parents behind the curtain watching,” he adds. “Also, those nurses can’t stop my mom! Like, Diana Ross just walks in.”

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Image zoom Evan and Ashlee Simpson Ross for Zadig & Voltaire Courtesy Zadig & Voltaire

Image zoom Evan and Ashlee Simpson Ross for Zadig & Voltaire Courtesy Zadig & Voltaire

Little Jagger is just as headstrong as her famous grandmother, having already developed her own fashion preferences and opinions to match.

“I love dressing Jagger. It’s so much fun for me!” says Simpson Ross, 33, adding that she’s saving a collection of “vintage Chanel dresses” for Jagger when she grows up. “If she doesn’t like something, she’ll check it out in the mirror and tell me.”

Ross tells PEOPLE his wife’s 9½-year-old son Bronx Mowgli “is getting his own sense of style,” adding of Simpson Ross, “She’s very focused on dressing Jagger.”

Image zoom Evan and Ashlee Simpson Ross for Zadig & Voltaire Courtesy Zadig & Voltaire

RELATED VIDEO: Ashlee Simpson Thanks Evan Ross for “Giving Me the Best Love” in Sweet Wedding Anniversary Tribute



The couple have their own unique suggestions for when they need a parenting timeout (“Sky Zone,” says Ross, while his musician wife chimes in, “Or nap time!”), but are on the same page when it comes to homework.