The Telegraph broke the news Friday ... reporting that they've been told by their Buckingham Palace sources that the King and co. were recently made aware of JB's intentions -- namely, not being in attendance as one of the many heads of state that are scheduled to show up.

That doesn't mean there won't be someone on his behalf, though. Per the UK outlet, he's mulling sending either his wife, First Lady Dr. Jill Biden, or his Veep ... Kamala Harris.

In addition to Jill/Kamala, there'll also be a formal U.S. delegation -- which will presumably include ambassadors, diplomats and other personnel ... the White House has said they'll announce those names in the coming weeks.

As for why Joe's bailing ... the word is, he has prior commitments -- although it's unclear what exactly. Here's the thing, the Telegraph reports it's no harm, no foul as far as Charles is concerned. In other words, he isn't taking it personally ... as no U.S. Prez has ever attended a British coronation, so it's not like POTUS is bucking tradition by failing to appear.

There's another thing to consider here, that some are reading into as it relates to Biden and his feelings about Charles and the monarchy at large -- perhaps he doesn't like 'em much.

There are reports that Biden's mother, who was of Irish descent, absolutely hated England (see history for why) ... which, if true, surely might've been communicated to Joe at some point. There's also the Harry and Meghan factor ... which could also be playing into this.

He's been pretty neutral on commenting about them -- but his ex-Press Sec., Jen Psaki, did publicly praise them for speaking up in the Oprah interview, saying JB felt that took courage.

In any case, Joe's gonna be a no-show.