She tweeted: "Phoenix has named our baby girl the cutest name,can't wait for you guys to hear it,soon ma peeps!!"
During her pregnancy, Mel had already asked for suggestions for unusual names for her first baby with husband Stephen Belafonte. Her suggestions were Sunny, River and Hunter.
Now the big question: is this a nickname or the real name?
If Mel's previous name choices - Phoenix Chi, now 12, and Angel, four - are anything to go by, this one's going to be a corker. But can it beat fellow spice girl Victoria Beckham's choice of Harper Seven?
Check out other celebs below who've named their children seriously silly names.
Did you let your older child choose the baby's name? Any suggestions for what Mel/Phoenix may have called their new addition to the family?
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