I am an only child.  I have no brothers or sisters.
Are you upset about that?
I suppose it is conceivably possible that i have a half sibling somewhere out there that i do not know about.
I think I actually do have one of those
Only child
An only child is a person with no siblings, either biological or adopted. 
Children who have half-siblings or step-siblings, either living at the same house or a different house - especially those who were born considerably later - may have a similar family environment to only children, as may children who have much younger siblings from both of the same parents (generally ten or more years).
Overview.
Throughout history, only children were relatively uncommon. From around the middle of the
humility and natural athletic ability and I think he has that great combination. You combine those two and you get someone who could be unstoppable.’’ Of all the praise, Ringer responded, “I have to give credit to how I was brought up. I grew up in a religious family and I know without God none of this would be possible for me anyway, so that definitely keeps me humble. My personality is not to boast and brag about the accomplishments and things I am trying to do. Actions speak