The countdown is on for the arrival of Chrissy Teigen and John Legend's baby boy — and their daughter Luna Stephens is also busy getting ready to meet her baby brother. In a cute new Instagram snap, Luna, 2, proved she is already the best big sister as she read The Brother Book with her famous dad.

"Prepping for a new arrival," John, 39, captioned the selfie with his adorable mini-me. Wearing a floral onesie, Luna was all smiles with the "All of Me" singer, who also cannot hide his excitement about becoming a father-of-two.

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Prepping for a new arrival!

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Chrissy and John announced they are expecting baby No. 2 last October with a gender reveal a few months after — and Luna has been anxiously awaiting her baby bro ever since. "You should see how loving and nuturing she is," Chrissy, 32, told E! News. "Even now, getting ready for baby boy, she has her baby dolls and the things she does with them… she'll feed them with a little bottle and give them pats on the back. It's so cute to see."

Before Luna's arrival, the couple opened up about their infertility struggles and revealed they underwent IVF to conceive. "It’s kind of crazy because even though you do all this planning and preparation, you take progesterone and inject your body and do all this stuff — and when I finally did get pregnant I was like, ‘Oh crap, are we ready?'" she explained to Self magazine. "I think it kind of doesn’t matter whether you do all that preparation or whether it’s a surprise. You still wonder if you’re ready. But then you hear from enough people that you’re never really ready, and you just go for it."

The Sports Illustrated model recently announced she has officially entered nesting mode so no more red carpets — but that means John and Luna won't have to wait much longer.