Regretfully

We regretfully reject your offer.

Regretfully it is not possible.

I was invited last week as well, but it was late so I regretfully turned them down.

Many a gentleman of the old school has been provoked to remark regretfully upon the under-bred manners and bearing of even the better classes in the modern industrial communities; and the decay of the ceremonial code—or as it is otherwise called, the vulgarisation of life—among the industrial classes proper has become one of the chief enormities of latter-day civilisation in the eyes of all persons of delicate sensibilities.

Members of the jury, regretfully I must declare this proceeding a mistrial.

Regretfully, the Japanese representative was eliminated at the preliminary stage.

Oleg regretfully told Rima that her family was dead.

I regretfully admit that I don't love you anymore.

I can't make you see your own shortcomings, regretfully so.

So after learning a great deal about iron founding and much more about pike fishing, one regretfully took leave of a shop full of kindly characters and proceeded to a worse lot of odours in the brass foundry.