Raquibul Hassan was only 16 when selected as 12th man for Pakistan vs New Zealand, 3rd test in Dhaka, November 1969. He would have gone on and played full tests if he had remained a Pakistani citizen. He chose not to. Andrew Miller quotes him in the article below: "To lose a Test career? That is nothing".
There are others who believe the only reason he was named on the Pak squad was a cynical last-minute attempt by the Pakistanis to show that they were being inclusive in their team selections. Not one East Pakistani Bengali-origin player was selected prior to Raquibul. Lack of talent? Coincidence?
History doesn't do much to record 12th men. But Raquibul was always much more than that.
Here are the links:
Andrew Miller U-19 World Cup article
Pak vs New Zealand, 3rd Test, Dhaka, Nov 1969