It has since attracted almost 1 million 'likes' and thousands of comments congratulating the mum.
Earlier this year, the American model told The Wall Street Journal magazine both she and Justin were ready to give their 17-month-old son Isaac a sibling.
"I would get pregnant yesterday if I could," Ashley told the publication in February.
"I've 'accidentally' had unprotected sex while I'm ovulating just to see if I can [get pregnant] while I'm breastfeeding."
A few months later while she was guest hosting The Ellen DeGeneres Show Ashley revealed she was "currently working" on conceiving her second child.
Ashley and Justin, 31, a cinematographer, married in 2010 after meeting at church.
The model said they didn't have sex until they were married, with Ashley telling Elle magazine she wanted to wait until they were wed as "abstinence was a firm commitment to his faith".
She told the magazine the secret to her happy marriage was to "have sex all the time".
"Even if you don't feel like it, just have sex," Ashley explained. "I have found that if we haven't had sex, we get snippy, and then if we are having sex, we're all over each other."
In 2020, Ashley then gave birth to her first child, Issac, saying: "Meeting our son has made our hearts incredibly full and we can't wait to introduce him to you."
She has since shared candid posts and videos about her experience with motherhood.
"People tell you, people try to explain it to you, but you don't know love until you have a child of your own like that," she said in a YouTube video.
"I cannot believe how fast this year went, watching everything: how you [Issac] turned on your own and crawled on your own and started talking and walking on your own.
"And how we play with the ball, kicking and throwing, and how your Daddy loves you so much and how much I can see you love him back. It's just this beautiful bond."
