Anias and Jadon McDonald, the 13-month-old twins who were conjoined at the head since their birth last fall, were successfully separated in a surgery conducted at the Children’s Hospital at Montefiore Medical Center in Bronx.

After a 16-hour surgery, the twins’ mother Nicole McDonald wrote in a Facebook post that she was finally feeling at peace. However, she admitted that her heart was yet aching due to the uncertainty over the twins’ future.

In the Facebook post, she wrote, “TWO SEPARATE BABIES!!! And yet I ache with the uncertainty of the future. I didn’t cry until the surgeons left the room. I was barely able to even utter the words 'thank you' because of the pit that still sits heavy in my stomach. We are standing on the brink of a vast unknown.”

She also revealed she already had one toddler in March 2015, when she discovered that she was pregnant. She and her husband were shocked when her ultrasound revealed that her twins were conjoined at the head. The odds of such a conjoinment are just 1 in 10 million.

According to CNN, which provided a live broadcast of the ambitious surgery, it was only the 59th of its type operation performed in more than six decades.

As the next several months will be very crucial for the twins’ recovery, doctors will keep an eye on how they recover after the separation and if any complications develop.