Translation

後悔して / 残念そうに / 申し訳なく思って

Meaning

Regretfully means in a way that shows personal regret, sadness, or apology about what someone is doing or has done. It often describes a person's tone or decision. The learner trap is using it when the fact is simply unfortunate; regrettably is often better.

Examples

• 彼は残念そうに申し出を断りました。
  He regretfully declined the offer.
• 彼女は以前の発言について後悔しながら謝罪しました。
  She apologized regretfully for her earlier comment.