Kate Middleton's feelin' the love from every corner of the globe ... including from a prominent member of her own family who had a close connection to Princess Diana.

Charles Spencer -- the late Diana's brother -- posted a message of support to Kate Saturday following her bombshell cancer video announcement Friday.

The 9th Earl Spencer shared a screengrab of Kate's appearance and kept the caption short and sweet, writing, "Incredible poise and strength."

It's a pretty simple message from Princess Di's bro ... but, meaningful nonetheless. Remember, Diana was always applauded for her own poise as she went through her messy divorce from King Charles in the early 1990s.

And, Spencer even publicly compared the media scrutiny around Kate's stepping away from the spotlight to media attention around Diana before her death earlier this week -- making a more direct comparison between the two women.

Of course, Spencer isn't the only family member to send their messages of support out wide for Kate ... with the king and his wife Queen Camilla also making a public statement lauding Middleton's courage while Prince Harry & Meghan Markle even tried to reach out privately to the Princess of Wales.

Kate, of course, never got to meet Diana because the late princess was killed in a car crash several years before she started dating William.