The 28-year-old model and the Maroon 5 rocker already have daughter Dusty Rose - who celebrates her first birthday later this month - together, but the pair are already getting ready for their brood to expand as they have revealed they are once again expecting.
Behati took to Instagram on Wednesday (13.09.17) to confirm the happy news as she shared a photo of her burgeoning baby bump.
She captioned the snap: ''ROUND 2..... (sic)''
Adam, 38, has yet to publicly comment on the news, with both his Twitter and Instagram profiles having remained silent since the start of September.
However, a source told 'Entertainment Tonight' that the 'Sugar' hitmaker is ''over the moon'' at the news.
The insider said: ''He and Behati want lots of kids, and they want them close in age. Adam is over the moon, as is Behati. They are in love with Dusty and can't wait to make her a big sister. Adam has already been making sure his schedule next year has time to allow for him to take off work and be with the new baby.''
The pair - who married in 2014 - are already set to shower their impending arrival with love, as Behati recently revealed she feels ''next level love'' for Dusty Rose, and never thought she could possess such ''intense'' feelings for another person before the tot was born.
She said: ''I think the fact that you could love a person more than you ever thought.
''I love Adam, and when you get married and you fall in love with someone, you think that there's no greater love than that love. And then you have a baby, and it's just next-level love.''
And Behati was ''surprised'' to find her heart swelled even more when their family expanded from two to three.
The South African star continued: ''I think I was surprised by that because everybody always tells you that, and you're like, 'Yeah, yeah, whatever.' I see how much more you can love.
''You think there's a limit to love - like, 'This is the thing that I love the most' - but honestly, I think what surprised me most is how intense that love is, and also how hard, at times, it is.''
His new album Underneath It All is out now.