We have learned that my two children have another half sibling. A boy only about 6 months younger than my son.
So counting my two kids, and "T", the little girl we met twice over the last few years, we know of 4 children born from our donor. I plan on referencing the new half sibling as "Z".
And wait the news continues. Both T and Z and their moms are coming to NYC the first weekend in December ! All four kids under one roof. When Z heard about T and my kids he asked his mom when he can meet everyone else and somehow Z's mom got all of us talking and it is happening. Amazing.