sincerely

sincerely /sɪnˈsiɚli/ adverb
sincerely
/sɪnˈsiɚli/
adverb
Britannica Dictionary definition of SINCERELY
1 
: genuinely or truly : in a sincere or truthful way
2 
◊ Sincerely, yours sincerely, and (chiefly US) sincerely yours are often used at the end of a formal letter before the sender's signature.