Dwayne 'The Rock' Johnson and his long-time partner Lauren Hashian are expecting a baby girl.

Dwayne Johnson and Lauren (Instagram)

Dwayne Johnson and Lauren (Instagram)

The 'San Andreas' star and Lauren announced they are expecting their first child together in September and the wrestler-turned-actor has now taken to his Instagram account to reveal they're preparing for the birth of a girl.

Dwayne posted a picture of himself cradling Lauren's baby bump, and captioned the image: "I was raised by and live with amazing and strong women, so the universe felt we needed one more... IT'S A BABY GIRL!! THANK YOU guys so much for the awesome support and love you've sent @laurenhashianofficial and myself from around the world. We're so grateful for this blessing and thrilled to share the news with y'all. (sic)"

Dwayne already has a 14-year-old daughter, Simone Alexandra, with his ex-wife Dany Garcia, and a source close to the Hollywood star recently said he's "thrilled" at the prospect of becoming a father for the second time.

The source explained: "Dwayne and Lauren couldn't be more thrilled. They've been rock solid for about nine years now and felt it was time to expand their family.

"Lauren's brother is also expecting a baby, so the entire family is overjoyed!"