Paul the 12th Apostle?

Today's question comes from one of our young people:

Was Paul an apostle, and considered one of the twelve? How could he be if he did not see the Lord like the others?

I tried to keep the answer brief, so I didn't cite all the verses. But here it is: First, there were 12 apostles. But Judas was a bad apple, and wasn't genuine. So, after he betrayed the Lord, there were 11. Then after Jesus ascended to heaven, the 11 picked Matthias to become the new 12th apostle. He had been with them throughout Jesus' ministry and saw all the things they did.

Now, as for Paul, he definitely was an apostle (1 Timothy 2:7). But he is number 13. His selection was different than the others, because he saw the Lord on the road to Damascus after Jesus had already gone back to heaven (Acts 9:3-7, 17). He saw Jesus at other times too (Acts 22:18, probably also 2 Corinthians 12:4). He received the good news directly from the Lord (Galatians 1:12). His ministry was also somewhat unique, for God sent him to the Gentiles to preach Christ (Romans 11:13).