Country singer Jason Aldean and wife Brittany welcomed their first son together, Memphis, to the world seven months ago. 

But they're already getting to work on growing their family. 

On Tuesday, the couple posted a photo to Instagram of Memphis wearing a “big brother” onesie, to let fans know that they're expecting a second child together.

Jason, who also has two older children from a previous marriage, wrote: 

Sup everybody....... guess who is gonna be a BIG brother! #thisdude#aldeanpartyof6

Many fans applauded the couple on their upcoming bundle of joy, but some were surprised that the two opted to welcome another child so soon after their first.

One Instagram user wrote: 

Another One??? Within 8 months??? WHAT!!! TBH(not being a hater) But i don't think your ready it's gonna be up 24-7 with 2 infants.

Another said that it may be “too soon” for the mom, because Memphis was “just born.” But another user jumped to Jason's defense.

They wrote: 

Jasonaldean , it makes sense to have your children in a young age. And so fast as possible , so that the children can enjoy each other throughout their lives. Good luck with your pregnancy to you all...

In December, Brittany told People that she wanted to have her children close together and was considering a gestational surrogate. She said: 

“The sooner the better. You’re already doing the diaper thing, you’re already doing everything. Why don’t we just knock it out instead of getting out of that time frame, and then having to start all over again?”

Before Memphis, the couple struggled to conceive naturally and underwent in vitro fertilization. 

Brittany has not revealed whether she is pregnant, or if the couple is using a surrogate.

But if she is carrying a child just seven months after giving birth, their child may be at increased risk of autism, according to Mayo Clinic.

Second-born children are more likely to have autism if they are born less than 12 months after the first child.

The mother may also not be physically ready to have a second child, which could impact things like breastfeeding.

It is recommended that mothers wait between 18 months and five years between each pregnancy.

However, it's possible Brittany may just not have disclosed their use of a surrogate.