mendaciously

adverb1

1. •
   In a lying or deceitful manner.

   • As a politician, he was very adept at speaking mendaciously in public.
   • I don't think I'm going to buy what she just told me. Her gestures, eye movements, and hesitancy in her tone raised some substantial red flags. Therefore, I have reason to believe she was giving an excuse mendaciously. If you could've witnessed this, you'd know it too!