Zendaya was all smiles in L.A. Monday night as she made her first public appearance since TMZ broke the news about her engagement to Tom Holland.

The actress could barely contain her excitement as she arrived at a special screening for her popular film, "Challengers," at the Pacific Design Center in West Hollywood -- and, while she was there, she showed off her new diamond ring from Tom.

Yet, Tom was nowhere in sight, but Zendaya was still in good hands as security directed her past the paparazzi so she could go inside and watch the movie.

Check out photos obtained by TMZ ... Zendaya is grinning from ear to ear and looking like a million bucks in her stylish black outfit -- and, why wouldn't she? She's preparing to tie the knot with one of Hollywood's biggest actors -- and hunks!

As we first reported Monday morning ... Zendaya got engaged to Tom between Christmas and New Year's at one of her family homes in the U.S.

Our sources say Tom knelt on one knee to pop the question and put the big rock on Zendaya's finger. We're told it all went down in an intimate setting with no family present.

Next step -- the wedding!