how to tell my child his dad is not his real da

my little boy is 5 years old, i have been in a realationship with the man he calls dad for 4 an half years we have 2 children together. My partner has accepted my son as his own which was brilliant of him and he dosent treat him any different to the others. my problem is i came from a broken family an i was lead to believe my dad was my dad when he wasnt he was my step father i got told by a non family member as my mum didnt think i was old enough at the time to be told they went behind her back i just want whats best for my boy an how best to tell him. The other day i was on a social network site and i was looking at pictures of my sons biological dad's wedding when my son asked "mummy is that my daddy standing with grandad steve" (he calls is bio dads dad grandad steve) and i asked him why he thought this and he replied "cause mummy i look like him he got the same big ears as me!" could this of been my oportunity to tell him?? it could have been but i was shocked at the fact he came out with that out the blue

[Kevin Kennedy, Ph.D.]

Yes, you should tell him. Be clear and simple, saying that yes, indeed, Grandad Steve's son is his father. You needn't say anything else. Just be avaialbler to respond to any of his questions or concerns, but don't expect many at this young age.