Elton John and David Furnish are planning to have second child via surrogate so their son will have a sibling.

The couple became parents to 13-month-old Zachary on Christmas Day 2010, and have doted on the tot ever since.

Despite expressing fears his son will be "stigmatized" for having two gay fathers, filmmaker Furnish has revealed the pair is eager to have another child later this year depending on their schedules.

He tells London's Evening Standard, "I would like Zachary to have a sibling. I think he would be better with a sibling than on his own. It's something we talk about all the time. But in terms of when, where and how, nothing's decided yet."

"I think we are going to wait 'til this summer. Our life is always like a treadmill with Elton constantly working and touring. But when we go away to our house in France, that's when we sit back and go, 'OK, how is this working, how are you feeling?'"

Furnish adds the couple is considering using the same surrogate who carried Zachary, and they will not know who the biological father is.

He explains, "We could go back to the same egg donor, so biologically there would certainly be a connection between brother and brother or brother and sister."

Slideshow: The Eccentric Elton John