"So grateful and in awe of this time," Hashian wrote on Instagram.com. "To experience creating a little life is just incredible."
The 31-year-old singer-songwriter added: "This beautiful cycle of life and womanhood beginning again. And like Big Daddy says - Couldn't be prouder of all the kick-ass women she's going to have around her! And men of course ;)..."
Hashian joked about the baby's size, writing "Lets just hope big daddy doesn’t equal 20lb baby."
Johnson also has a 14-year-old daughter, Simone Alexandra Johnson, by ex-wife Dany Garcia.
Johnson and Hashian met in 2007 -- while he was still married.