Alec and Hilaria Baldwin are expecting a baby boy.

Hilaria and Alec Baldwin

Hilaria and Alec Baldwin

The 57-year-old actor - who already has Carmen, two and Rafael, eight months together with his wife and daughter Ireland, 20, from a previous relationship - is set to welcome his fourth child into the world.

Taking to Instagram, Hilaria announced proudly: "Ireland, Carmen, Rafael, Alec, and I are excited to share with you that we are going to have another addition to our family. A little boy coming this fall #366daysoflivingclearly #HilariaLCM (sic)"

Meanwhile, Alec previously revealed he wouldn't mind having more children and said the couple are just leaving it in the hands of fate if they fall pregnant again.

He shared: "When a baby shows up that person was meant to be here. And if there is one more meant to be here, or two more meant to be here, so be it ...

"I love my wife more than anything. I love our family, I'm very happy. I've never been happier before in my life ... Even my daughter Ireland has been visiting and we see her falling more in love with Carmen every day. It's really fun. This is the best time of my life and I owe it all to my wife, truly."