"Princess Bride" star Cary Elwes got right up to the altar with the guy who was going to buy his Malibu home, and then jilted him -- so now he's getting sued for backing out on the sale.
According to the docs ... Tris Felder says Elwes agreed to sell the pad to him for $1.7 mil -- but when it came time to deliver the $51k deposit ... Elwes rejected it and called off the whole deal.
In the suit, Felder admits he doesn't have a signed purchase agreement -- but says Elwes did sign the counteroffer letter ... and that's enough to make the sale legit. If he doesn't get the keys ... he wants at least $500k in damages.
In other words ... "You killed my father. Prepare to die."