Exclamation in speaking task

I am looking for words that have the same meaning of saying 'Really?' in speech but has a more formal and better feeling.

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I found some synonyms for really. But I don't think they can replace Really:

easily
certainly
absolutely
indeed
well
actually
unquestionably
surely
literally

honestly
truly
undoubtedly
genuinely
assuredly
de facto
in effect
indubitably
of course

positively
precisely
verily
legitimately
admittedly
as a matter of fact
authentically
beyond doubt
categorically

for real
in actuality
in fact
in point of fact
in reality
no ifs ands or buts
nothing else but
unmistakably