A US mother’s search for her daughter’s original adoption ad as a Christmas gift has ended with the joyous discovery that she has a twin sister.

Wisconsin mum Jennifer Doering recently embarked in a search for daughter Audrey’s “finding ad” – an newspaper advertisement posted by the Chinese orphanage where Audrey was adopted, local broadcaster KNDO reports .

It was Ms Doering’s wish to present Audrey the newspaper clipping as a gift for Christmas.

Over the course of his search however, a man charged with tracking down the information made the surprising discovery of a photo showing baby Audrey sitting on a woman’s lap alongside a second baby.

Both girls share a remarkable resemblance to one another.

Within days, Ms Doering was able to learn that the second child was not only Audrey’s hitherto-unknown twin Gracie, but that she had been adopted by another US family, the Rainsberrys, and was now living in Washington state.

Mother Nicole Rainsberry said she had had Gracie’s finding ad along along but had not realised that the girl in the photo was in fact Gracie’s sister.

She said watching a video of Audrey really brought home the girl’s physical similarities.

“Not just do they look alike, their voices are the same. Their mannerisms are the same,” she said.

The revelation proved a particularly emotional one for Gracie, who said it left her in tears.

Audrey and Jennifer have since shared a video chat and intend to meet in the near future.

Audrey and Gracie's "finding ad". (KNDO)