Madonna has a superfan ... ex-husband Sean Penn, who was smack dab front and center at her Wednesday night concert in Vancouver.
Penn took in the show alongside Amy Schumer, who opened for Madge earlier on tour, but Penn only had eyes for his ex-wife.
It's the second time in a month he's caught his ex on the road, the last time being this past September in NYC.
All that staring might have paid off ... Madge dedicated the song "Secret" to a "special guest." The lyrics start, "Things haven't been the same since you came into my life, you found a way to touch my soul and I'm never, ever, ever gonna let it go..."