King Charles proudly unveiled the first official portrait of himself since his coronation last year -- and let's just say ... the internet's reaction is more fire and brimstone than royal praise.

HRH was at Buckingham Palace Tuesday with Queen Camila, where he pulled down a massive curtain to reveal the highly-anticipated portrait -- which features a fiery red backdrop, much to shock of royal fans and normies everywhere.

Even Charles' finest Welsh Guards uniform for the painting couldn't distract from the real star of the show -- that bold, brash backdrop, which led to a tidal wave of online critiques/jokes.

One X user tweeted, "Who approved King Charles III's new portrait cuz it looks like he's in hell?!" Others echoed a similar sentiment ... saying it looked like he'd accidentally wandered into in the fiery pits of Dante's inferno.

In fact, you could argue the whole thing was a full-blown roast session ... with some saying Charles looked "villainous," while others saying he appeared to be drenched in blood ... some even going as far to say the whole thing looked satanic.

Obviously, it's probably not the feedback Jonathan Yeo wanted after the 3 years it took for him to paint it at his London studio -- which also included 4 sit-downs with Charles himself.

Nonetheless, King Charles' portrait in all its fiery glory will be on display at London's Philip Mould Gallery for a month-long exhibit. After that, it's off to the historic Draper's Hall, once owned by none other than King Henry VIII himself.