10/20 River spot with Nut flush on paired board

[T_Mac]

Villain is Elky. We've been playing on multiple tables for a few days, but have never really gotten involved in any big pots. I felt good about my hand on the turn, but when the river hit he INSTANTLY went allin...There was a hand a little while ago where he semi-bluffed the flop and turn with a flush draw, then pot bet the river when he missed and got called. The fact that the river was a 4th spade made this a little harder for me to fold, though him representing a big spade here might be ridiculous to assume considering my raise on the paired turn? Pretty simple question on the river, call or fold?


PokerStars ($20 no limit). Hand converted by Check Raised hand converter

Preflop (6 players): Hero is SB with
BTN raises $80.00.
HERO calls ($80.00) [2.38:1].
1 fold.
UTG calls ($80.00) [3.38:1].
2 folds.

Flop (13.5 bets ($270) in pot, 3 players):

BTN checks.
HERO checks.
UTG checks.

Turn (13.5 bets ($270) in pot, 3 players):

BTN bets $180.00.
HERO raises $580.00.
UTG folds [1.78:1].
BTN calls ($400.00) [3.58:1].

River (71.5 bets ($1430) in pot, 2 players):

BTN bets $13866.30.