Grammar question: Usage of regret

[monica]

Hello. I'm checking a book on the grammatical usage of "regret". There is the following sentence:
I regret (the fact) that she has left
The book says normally we can omit "that" after regret. But, in my opinion, "I regret she has left" sounds funny. So am I wrong or is the book wrong? Or is simply the example that doesn't work? Thank you

[Mister Micawber]

.
'That' can be omitted. The sentence is clear to me without it.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber