"Christmas came early! Within minutes of being born she was laying on daddy's chest. And being a grateful man takes on a whole new meaning," he wrote.
Johnson, 43, announced last month that Hashian, 31, was pregnant. This is the second child for the former wrestler, who has a teenage daughter, Simone, with his ex-wife Dany Garcia. Shortly after the split, Johnson began dating Hashian, a singer-songwriter.
"I've lived with my longtime girlfriend, Lauren Hashian, going on, like, eight, nine years now," he told Esquire this past June. "We spend a lot of time with my daughter in Florida, Simone, who's 13. We do these stories and we talk so much about the business end, the success end, but then Lauren isn't mentioned and my daughter isn't mentioned.
"I always like making sure we find the balance and my home life is in there and Lauren Hashian is in there and my daughter is in there," he continued. "You gotta get the better half in there. With all the cool s--- and success that I've been lucky enough to get? That doesn't happen unless the home life is solid."