Jason Derulo -- Suck It Jordin ... I'm The King Of My Own Castle Now

Jordin Sparks may be a damsel in distress ... but now that she's trashed him, she won't be welcome at Jason Derulo's new castle.

Jason bragged about his new medieval digs -- insinuating he doesn't care that Jordin is now trashing him -- by tweeting that he's moved on to bigger and better things: "I bought myself a castle 2day!! No big deal."

Jason isn't directly responding to Jordin's new single in which she essentially calls him an ingrate and an a-hole. But he started it by putting her on blast for allegedly pressuring him to tie the knot.

As for his $3 million acquisition deep in the San Fernando Valley ... it's 10,000 square feet, outfitted with turrets, a dungeon, a basketball/tennis court, and a lap pool -- standard issue for land barons.

It's like Henry VIII moved to Tarzana ... which sounds like a CW show.