Gnabry became the first player to score four goals in the second half of a Champions League game as Bayern Munich defeated Tottenham 7-2 to take charge of Group B.
Pulis secured the signing of Gnabry from Arsenal on a season-long loan deal in the 2015/2016 season but sent him back to the Gunners just six months later after being unimpressed with his quality.
Speaking in 2015, Pulis said: "[Serge Gnabry] just hasn't been for me, at the moment, at that level to play the games [for West Brom]."
Gnabry played just 12 minutes of Premier League football during his short stint under Pulis at the Hawthorns before Arsenal moved him on to Werder Bremen for a meagre transfer fee of £5m.
The 24-year-old has since improved to make the move to Bayern Munich, and after seeing Gnabry produce a scintillating display on his return to England, Pulis had nothing but praise for his former protégé.
Pulis told Sky Sports: ‘Well, I’m amazed. We had him at West Brom, we took him on loan and we could never get him fit. I think he even got taken off in an Under-21 game. He went back to Arsenal, they sold him on.
‘He was a good kid, a nice kid, didn’t mind him at all. He’s fulfilled his potential.
‘You could knock me over with a feather having worked with him at West Brom and seen him there to what he’s done is absolutely amazing.
‘When people show what they can really do and really knuckle down and become so good as he’s done, it’s absolutely fantastic. The kid’s done fantastic.’
