Faith Williams, the month-old conjoined twin who survived a lengthy surgery to separate her from her sister, died on Christmas Day, London's Great Ormond Street Hospital said.

Her doctor, Agostino Pierro, said in a statement that while Faith's death was very sad, it was not unexpected.

Click here for photos of conjoined twins.

"We were always clear that Faith was very sick," he said. "She required the full range of skills of our intensive care staff, and underwent a number of further procedures. However, she succumbed to the complexities of her condition."

Faith's sister, Hope, died on Dec. 2, hours after doctors completed an 11-hour operation to separate her from her twin. Pierro said at the time that Hope's lungs were too small to support her breathing and circulation. He said then that Faith's chances of surviving were about 50 percent.

Faith and Hope were born Nov. 26, joined from their chests to the lower part of their stomachs. They had separate hearts, but shared a liver and intestines.

The babies' mother is 18-year-old Laura Williams, who is Britain's youngest-ever mother to give birth to conjoined twins.