And Spock never had a human sister either until recently.
There's not telling you friends about a relative and then there's no historical record of a relative. The idea that his then 70 something son wouldn't be mentioned when he took off to Romulus and was feared a traitor and Sarek died is...a bit much, even for Spock.
I never have gotten the idea then or now that Saavik screwed a brainless Spock clone. I kind of sort of see why people might think that now, but no. Just no.
Then how did he survive the ponn far?