Once.

 Watkins-Pitchford, Bluebells Flowered in the Clearings of the Big Wood, 1960

"I have come back once more to you all once more …" Pan paused, and in the silence not a foot moved or a wing rustled, "and then I shall indeed be gone until that day when we shall all return, yes, all, gnomes and wild forgotten things alike, to the land where once we lived."

B.B., from The Little Grey Men