50NL River the nut flush on paired board

PokerStars No-Limit Hold'em, $0.50 BB (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

BB ($90.45)
UTG ($13.10)
MP ($49.25)
Button ($54.60)
Hero ($49.25)

Preflop: Hero is SB with Ahttp://www.flopturnriver.com/phpBB2/...iles/heart.gif, 5http://www.flopturnriver.com/phpBB2/...iles/heart.gif.
2 folds, Button raises to $1, Hero calls $0.75, 1 fold.

Flop: ($2.50) 9http://www.flopturnriver.com/phpBB2/...iles/heart.gif, 8http://www.flopturnriver.com/phpBB2/...iles/heart.gif, 8http://www.flopturnriver.com/phpBB2/...es/diamond.gif (2 players)
Hero checks, Button bets $1, Hero calls $1.

Turn: ($4.50) 2http://www.flopturnriver.com/phpBB2/...miles/club.gif (2 players)
Hero checks, Button bets $1.5, Hero calls $1.50.

River: ($7.50) 3http://www.flopturnriver.com/phpBB2/...iles/heart.gif (2 players)
Hero bets $5.5, Button raises to $11, Hero ???

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Villian is an unknown.

What's your play here?

Got a read for us? What do you know about him?

BN vs Blind, no way I fold here.
Given the stakes it could be an over-pair or trips.

He seems like a mega-donk, I think I'd 3 bet the river and call a push. Calling is acceptable as well. Anything not involving the "fold" button is good.