tough river spot with topset in 3bet pot

[TheLoon]

Villian is almost unknown. But seems LOOOOOOSE passive.
EverestPoker Game #2194502983: Table Dili-17 - $0.50/$1 - No Limit Hold'em - 14:07:07 - 2007/10/10
Seat 1: TheLoon ($129.60)
Seat 3: mathijs84 ($119.60)
Seat 4: Ice51 ($153.75)
Seat 5: diego2000 ($230.05)
Seat 6: sponge.bob ($95.50)
diego2000 posts the small blind of $0.50
sponge.bob posts the big blind of $1.00
The button is in seat #4
*** HOLE CARDS ***
Dealt to TheLoon[Qd Qh]
TheLoon raises to $3.50
mathijs84 folds
Ice51 folds
diego2000 raises to $11.50
sponge.bob folds
TheLoon calls $8.00
*** FLOP *** [Tc Qc 8d]
diego2000 checks
TheLoon bets $13.00
diego2000 calls $13.00
*** TURN *** [Tc Qc 8d] [Jd]
diego2000 checks
TheLoon checks
*** RIVER *** [Tc Qc 8d Jd] [4c]
diego2000 bets $50.00
TheLoon ????

He bets pot