Jason Aldean's wife Brittany explains how their 2 kids were almost twins

Brittany and Jason Aldean's 2-year-old son, Memphis, and 20-month-old daughter, Navy, share the same big blue eyes and golden blond hair color.

They could have shared a birthday too.

"FUN FACT: Both of our babies are IVF babies," Aldean, 32, began in an Instagram on Monday. "We almost put Memphis and Navy in at the same time because after our long infertility journey, multiples seemed AMAZING to me."

But in the end, Memphis was transferred first. He was born in Dec. 2017, while Navy arrived in Feb. 2019.

"How crazy to think my babies who look almost identical could have been twins?" Brittany wrote.

Brittany and her country star husband struggled for more than a year to conceive their first child. (Jason, 43, is also a dad to daughters, Keeley, 17, and Kendyl, 13, from his previous marriage.)

"The IVF was probably harder than the actual pregnancy, for me, because it was such a roller coaster and so difficult," Brittany revealed on the "Babes and Babies" podcast in 2018. "It's such high highs and such low lows, and no one really knows that you're going through it all so you have to just put on a game face and pretend that you're not giving yourself shots in your stomach every day, all day."

Brittany, who was diagnosed with endometriosis during the emotional journey, considered hiring a surrogate at one point.

"We would do a transfer, which is basically where they would implant an embryo, and then it wouldn't take. So for a ten-day period, you would think, 'Oh I think I might be pregnant,'" she shared. "They give you a blood test at the end of the ten-day period and you're not. So in your mind, it's almost like you've had a little bit of a miscarriage, because you expect to be pregnant and you're not. That happened to us multiple times."