Substitute

[Zoochy]

After a basket a Team calls a 60 second Time out. After 30 seconds ALL 5 players for Team A come onto the court. An official is by Team B's bench when the 45 second horn sounds. He tell the bench 1st horn. A few seconds later a substitute from Team A reports to the table and stands at the scorers table. The 2nd horn sounds when Team B is breaking the huddle. As Team B and the official are moving onto the court, the official notices Team A's substitute. He beckons the sub into the game . The sub takes a few steps onto the court and then the Official realizes the substitute player SHOULD NOT not be allowed.
Per rule, what should the Official do?