The former Spice Girls singer explained her bandmate - who already has three sons, Brooklyn, 12, Romeo, eight, and six-year-old Cruz, with her husband David Beckham - is "thrilled" to be finally adding a baby daughter to her brood.
She exclusively told BANG Showbiz: "Victoria is thrilled to be having a girl. She was very, very excited to let us all know.
"Her boys are absolutely lovely and beautiful - they're beautiful boys - but them having a little sister is a dream come true. She's going to be the best looked after little girl in the whole world."
Mel - who was also joined in the five-piece girl band by Geri Halliwell, Emma Bunton and Mel B - also thinks Victoria and David's daughter, who is due to be born on July 4, will be taking over the 37-year-old star's fashion empire in the future.
Speaking at the launch of Virgin Active's London Triathlon Team this week, Mel added: "I'm sure she's going to be very stylish if she follows in her parents' footsteps - they're both very fashionable people. She'll be taking over that fashion empire in no time!"