Sir Elton John and partner David Furnish have admitted they have "no clue" which of them is their new son Zachary's biological father, because they both contributed to his conception

Zachary Jackson Levon Furnish-John was born on Christmas Day, weighing 7lb 15oz via a surrogate mother. In an exclusive first interview since the baby's birth, David told OK! magazine: "We both contributed. For the time being, we don't have a clue who the father is."

The 48 year old film maker continued: "We look at him every day and at the moment he has Elton's nose....neither of us care. He's our child," he added.

The couple used eggs donated from an anonymous donor, which were then mixed with sperm samples from them both, the Daily Express reports. They were then transplanted into the surrogate, who is known to be based in California.

Although the celebrity couple currently have no idea as to who actually fathered Zachery. Sir Elton, who was present at the birth, said they would be happy to do a paternity DNA test at a later date, if their son ever wants to know.

"We have no clue, but in the end if he wants to know, we can do a DNA test," he said.