Knight Rider” star Rebecca Holden and her record producer husband, Joel Diamond, got a rude awakening in the dead of night … an oak tree came crashing down onto their property, and cost ’em a car in the process.

Joel tells 360aproko … he and Rebecca were awoken late at night Friday by a loud noise literally tearing through their Calabasas home. It turned out to be part of a nearby 6-ton oak tree that had toppled over for some reason. We’re told the tree burst through their bedroom window … and also crushed three vehicles down below.

Unfortunately, one of those cars happened to be Joel’s prized classic Jaguar — the back end of which was absolutely demolished by the fallen timber. A total loss, no doubt. What sucks is Joel tells us he’d just gotten the whip back from an auto body shop 2 days prior.

Nobody was harmed, thankfully, but it sounds like a few of Joel’s friends were pretty impressed with the freak phenomenon. Singer Tony Orlando — known for his #1 hit, “Tie a Yellow Ribbon Round the Ole Oak Tree” — made a crack … saying out of all the trees he’d ribbon’d over the years, Joel and Rebecca’s was by and far the most outstanding.

Also … Joel says a top arborist in the area came through and priced the giant Oak, valuing it at around $250k. Talk about money growing on trees, huh???