The Manchester United legend was delighted to see the Arsenal defender on Friday night.
Neville managed the Germany international during his ill-fated four-month stint in charge of Valencia, which ended when he was sacked by the Spanish club last May.
The Arsenal man played no part in the 4-3 win over Leicester City, but he was on the pitch at full time to congratulate his team-mates on their dramatic victory over the Foxes.
And the 25-year-old bumped into his former boss who was working for Sky Sports' coverage of the clash.
Neville lost 11 and won 10 of his 28 games in charge of Los Che and has not yet returned to management.
It was a brilliant night for Arsenal, who came from 3-2 down to beat the Foxes as goals from Aaron Ramsey and Olivier Giroud in the final seven minutes flipped the match on its head.
The Gunners could've done with Mustafi in central defence as Arsene Wenger's side looked erratic at the best of times.