ever

No, say "He has never felt so embarrassed before" or "He was never so embarrassed."

The idea of being "so (anything)" is a unique experience, and since it was unique, it would always be the first time.

If it was the first time he had ever felt the emotion of embarrassment (lucky him!), then you could say "It was the first time he ever felt embarrassed." But that's not what you me

Yes. I understood but the problem is I want to keep the word "ever"

It was the keenest sense of embarrassment he had ever felt, perhaps?

Actually I think you were right. This is the most embarrassing moment he has had (which means he used to feel embarrassed before)
But we have to start with "it is" and end with "embarrassed"

He has never felt so embarrassed before.
=> It is.............................embarrassed.

Can you help me out?

sirius2012He has never felt so embarrassed before.=> It is.............................embarrassed.

It is a long time since he felt so embarrassed. (?)

Philip This is the first time he felt so embarrassed. (?)

I did. Like your sentence but we all missed the word "ever"
I have to put the word "ever" into the transformed sentence

And it has to end with embarrassed?
It is as embarrassed as he has ever felt... but that doesn't end the way you need it to.

Yes. There might be something wrong here
Thank you.

Glad to know that. Thank you.