Ashlee Simpson matured overnight when she learned she was pregnant with her and husband PETE WENTZ's baby, according to the pop star's father JOE.

The singer/actress is due to give birth any day now - but manager/dad Joe admits his little girl became a fully-fledged woman when she discovered she was to become a first time mum.

He tells People.com, "The day she found out she was pregnant, she became a woman.

"She's concerned about what she eats and how she prepares for the child and (details like) is the baby's room 'green' enough? It's a transformation you never expect as a parent - you pray for it, but never expect it. She's ready for this baby!"

And Simpson Sr. insists his son-in-law, Fall Out Boy rocker Wentz, is already showing signs of good parenting.

He adds, "Pete is the king of details, so he wants to make sure the baby's room is just right - the right colours, the right sheets, the right look. He's a great parent."

However, he is refusing to give away any clues about potential baby names: "I'm not allowed to give any hints. I can tell you it's not Joe. I wished, I tried, but it didn't work."