PNE's Gally says sorry for handball
The skipper dived to push away a 64th minute shot from Ayoze Perez on the line and was sent-off by referee Andrew Madley.
Matt Ritchie scored the resulting penalty to make it 3-1 on the night, with the Magpies going on to win 4-1 and clinch promotion to the Premier League.
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Hide AdGallagher tweeted: "Just want to apologise to everyone connected with PNE . I let everyone down . #pne #gutted."
The midfielder's two-handed save attracted plenty of attention on social media, both humorous and of a critical nature.
His red card will see him suspended for Saturday's final home game of the season against Rotherham United.
North End manager Simon Grayson said: "The red card was a reaction thing.
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Hide Ad"But it is something we are disappointed with because we have gone down to 10 men again.
"It happened at Leeds with Alex Baptiste getting sent-off and we have to be more disciplined in what we do.
"That was a key moment because at 2-1 we were still in the game but from then on it was more difficult."