The World's Desire by H. Rider Haggard

Presently, as she walked, Meriamun saw Rei the Priest and the veiled woman at his side, and she saw on the woman's breast a red jewel that burnt and glowed like a heart of fire. Then like fire burned the heart of Meriamun, for she knew that this was Argive Helen who stood before her, Helen whose shape she had stolen like a thief and with the mind of a thief.

"Say," she cried to Rei, who bowed before her, "say, who is this woman?"