The singer-turned-fashion-designer Victoria Beckham - who is famous for pouting at public events - has low self-confidence and that is why she rarely smiles.
She said: "I do have my insecurities. Maybe that's why I look a little bit serious. The kind of person who's going to stand on the red carpet and have the big grin - I'm not like that.
"I want to get in there, do what I've got to do, and get home to my kids."
Victoria - who has sons Brooklyn, 10, Romeo, seven, and four-year-old Cruz with soccer star husband David - has also refuted claims she is to pursue a movie career.
The 35-year-old star, who has previously mocked her own performance in 1997 movie 'Spice World', admits she doesn't have the talent to be an actress even if she wanted to.
She said in an interview with America's Elle magazine: "I know my boundaries - I know what I'm good at and what I'm not good at."
Meanwhile, Victoria and her sons celebrated Romeo's seventh birthday with a party in Los Angeles on Tuesday.
Romeo wore a suit jacket, tie and trilby to the party, while Brooklyn opted for a more casual grey T-shirt and jeans.
Perhaps keen to steal the show from his older brother, Cruz opted for a spaceman outfit, complete with red sunglasses and a star shaved into his hair.