Alec, 57, is also a father to 20-year-old daughter Ireland, from his first marriage to actress Kim Basinger.
Hilaria has always been creative in the ways she has chosen to share the happy news of her pregnancy in the past.
To announce the impending arrival of Rafael, she chose a photograph which featured Alec down on one knee holding Carmen up to her mum's bare stomach.
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Their little girl, looking cute in a pink coat and matching hat, was shown gently touching her belly while Hilaria looked on, holding the leads for the family's two dogs.
The sweet image was made complete with a colourful sunset taking place behind the growing family.
"'The sun has set on 2014 and on my year of daily #hilariaypd ....2015 is going to be very exciting as we are thrilled to announce we are expecting another little addition to our family!" she wrote at the time.
- AAP