Hours later the singer shared another photo showing off her burgeoning bump.
""Oooooh" Writing a song , (in my husband's boxers- my trousers don't fit anymore )🤗," Horner captioned the black-and-white shot.
Ginger Spice announced she was expecting with husband Formula One boss Christian Horner last month.
Horner is already mother to daughter Bluebell Madonna, 10, with her ex, screenwriter Sacha Gervasi.