The pair, who had been courting for five months prior to their wedding in Georgia on 18th April, revealed their baby is due in June next year.
Posting on Instagram, Grace shared that her sister, Morgan, is also pregnant.
The Grammy-nominated American singer, whose tracks include Hold Me, said: "My husband and I went to share our baby-on-the-way news with my sister and her husband and they surprised us with some big news of their own!
"We would have never expected or planned to be pregnant at the same time but we're so grateful to be on this journey together."
Jamie and Aaron - a model and actor - took the unusual step of saying "everyone's invited" ahead of their wedding at North Metro Baptist Church in Lawrenceville near Atlanta.
Grace continued: "Some may wonder if it's too soon for my husband and I to have kids (seven months married) or even too soon to announce it, but what seems like a surprise to some is God's perfect timing for us and never a surprise to Him.
"All four of us, and our crazy-excited extended families, are honored to celebrate these sweet, small lives (both due in June!!) and thank you in advance for your prayers with us as we celebrate them!"
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