John Legend and Chrissy Teigen are ''so excited'' that their daughter Luna is going to be a big sister.

The couple are thrilled to be expecting their second child and are so glad the news is out now after ''planning'' it for such a long time.

A source told People magazine: ''They have been planning for this for a long time. Chrissy is really excited to finally share the news.

''They are so excited to make Luna a big sister. They think Luna will do a great job with the baby and they're really happy to be expanding their family.''

Chrissy and John let Luna announce the happy news in a sweet Instagram post on Tuesday (21.11.17). In a video posted to the site, Chrissy points at her stomach and asks her daughter: ''Luna, what's in here?'' to which the little girl replies, ''Baby!''

And the couple's pregnancy is no surprise really as Chrissy had previously revealed she would love to be ''pregnant for the rest of her life''.

She gushed: ''I feel good, I feel good, we're still trying ... I'm going for I mean hopefully in the next few years because for me I really want to just knock 'em out. That's my dream, I want to just be pregnant kind of for the rest of my life. Not for the rest of my life, but the rest of my fertile life. So we'll see ...

''I probably think about it more than anybody. I cannot wait to have the biggest family. Everybody is curious. They're like, 'When are you going to do it? When are you going to do it? When's the process going to start?' It's so fun absorbing baby Luna right now. I think I'm enjoying my time absorbing and seeing everything - all her new little steps and new moments - and being there for them ... Every day it's something new with her. More than anything, I love seeing her little palette. She will eat anything and everything. I just think it's so fascinating. You give her the whisk and she knows exactly what to do the second you teach her. It's really cute.''