Sir Elton John has announced he will find out who his son's biological father is.

The 'Rocket Man' singer and his husband David Furnish became parents to four-month-old Zachary Jackson Levon through a surrogate mother on Christmas Day (25.12.10) and at first insisted they didn't want to know which of them was his real dad.

However, the 64-year-old star has now decided to carry out a DNA test in case Zachary ever needs to know who he is blood-related to for medical reasons.

Elton told the Daily Mirror newspaper: "Zac will have to know for his medical records. If it's David, I'd be very proud. It wouldn't matter to me - and vice versa."

He also revealed that the anonymous woman who carried his son sends the family her breast milk via air mail company FedEx.

Soon after Zachary was born, a friend of David's said the couple didn't plan to find out who was the biological father so the little boy would grow up to see his two parents as equals.

They said: "He and Elton made a pact that they are equal parents - no one will ever know who the biological father is."

However, Elton reportedly admitted that he hopes to be the one who shares his son's blood, although he would also be happy if David was Zac's real father.

Another friend added: "Elton was clear he wanted his bloodline to continue but also took on board advice that a younger man may be a more appropriate donor. It is a very complicated arrangement - but one forged by love."