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Selena Gomez couldn't be happier for her "bestie" Taylor Swift getting engaged to Travis Kelce ... gushing on social media to show her excitement.

The actress took to her IG story to re-share the viral shot of Travis down on one knee looking up at Taylor in a garden ... writing, "When bestie gets engaged" coupled with a heart-face emoji.

Selena chose the perfect song to match her mood ... playing Queen's "You're My Best Friend" over the pic.

To show how far they've come, the “Only Murders in the Building” star also reposted a 2009 tweet from Taylor to her ... saying, "Real love still happens sometimes. It's not just something we make up when we're nine. I have to believe that. You do too."

Above the old tweet is a side-by-side -- one shot showing Selena and her fiancé

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