The stepmother of Anna Allison, the 9/11 victim whose husband has offered to testify to save the lives of confessed terror mastermind Khalid Sheik Mohammed and his al Qaeda cohorts, was “shocked” to hear what her former son-in-law had done — and she wants to see the terrorists fry.

“I’d want to either see them executed or stand there with the gun myself,” Yvonne Williams told The Post. Williams, 76, said Anna’s late father also favored executing her killers.

But The Post revealed yesterday that Anna’s widower, Blake, 62, a death-penalty opponent, held a secret meeting at Gitmo with defense attorneys, offering to testify for mercy.

Blake said he’s under no illusions about KSM and his cohorts, but his deep opposition to capital punishment — rooted in his Episcopal faith — is “not situational.”