Search results in a table of private conversations

Question

I would like a help from you because I could not do with the topics I found on the internet.

I have a "Chat" table with the following fields:

And I’m using the following select:

SELECT b.`id`, b.`Fullname`, b.`Photo`, a.`Message`
FROM `Chat` AS a
INNER JOIN `Users` AS b ON b.`id` = a.`SenderBy`
WHERE a.`ReceiverBy` = '2'
GROUP BY a.`SenderBy`
ORDER BY a.`CreateDate`
LIMIT 20

That returns me the following result:

But the expected should be:

Anyway, what I was having done: Select the last messages received by Senderby group in descending order.