He's the boss of her heart!

Alyssa Milano and husband David Bugliari officially became parents on Tuesday morning, welcoming son Milo Thomas.

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And the New Year's Eve actress, 38, re-emerged on her beloved Twitter after the big news hit to proclaim her gratitude -- and her joy.

"Thank you for all the well wishes for my son Milo," Milano wrote. "My heart has tripled in size. I love him more than all the leaves on all the trees."

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An insider tells Us Weekly Milano was in labor for 12 hours before Milo arrived at 9:27 a.m., weighing 7 pounds and measuring 19 inches long.

It's the first child for Milano and agent Bugliari, who wed in August 2009.

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The couple hosted a baseball-themed baby shower Aug. 14 at L.A.'s Dodger Stadium with such boldfaced attendees as Holly Robinson Peete, Colin Hanks and Twitter founder Jack Dorsey.

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