The couple - who have three sons, Brooklyn, 11, Romeo, eight, and five-year-old Cruz - are believed to have found out after a 16-week scan the private Rivers Hospital in Hertfordshire, southern England, that they will be adding a healthy babygirl to their brood this summer.
A friend of the pair told The Sun newspaper: "David and Victoria are over the moon. This will be their last child and to be told they are having a girl is the icing on the cake for the Beckham clan.
"Victoria is 36 and David is thinking about life after retirement. For them, with a sister for their boys - who are growing up fast - this is the perfect family. All their dreams have come true. They couldn`t have wished for more."
Victoria has made no secret of her desire to have a little girl in the past, saying she would love someone to do girly activities with.
She explained: "I can imagine painting her nails, putting on make-up and choosing clothes with her.
"Everyone keeps asking if I`d like a little girl and I think, if I`m lucky enough to have another baby, that would be great."