what do i say to my dad who hasn't met me?

im 13 and i have never met my dad EVER so my mum says that i can send him a letter to see if he would ever want to meet me......im prepared for the worst but i have no idea what to say i mean what can you say "hey, you know that girl you went out with 13 years ago...yea shes my mum ur my dad wanna meet up?" i need something better than that...........please HELP!