Do you look like your brothers and sisters?

A middle-aged couple had two beautiful daughters but always talked about having a son.
They decided to try one last time for the son they always wanted.
The wife got pregnant and delivered a healthy baby boy.
The joyful father rushed to the nursery to see his new son.
He was horrified at the ugliest child he had ever seen.
He told his wife: "There's no way I can be the father of this baby!
Look at the two beautiful daughters I fathered!
Have you been fooling around behind my back?"
The wife smiled sweetly and replied:
"Not this time!"