My sons White and I'm mixed race ?

My girlfriend got pregnant last year and before my son was born we split up and stopped speaking. 6 months on we are trying to sort our relationship and I have met my son. The one problem is he is White with blue eyes. I'm mixed black and White and my sons mum is White. He doesn't look like Any off us. I have a 2 year old daughter and you can tell she is mine easily but my son has no resemblance. She said he's mine and I don't fink she would lie to me but he could pass for being a White baby and I don't no what to think. Any ideas on this ?