My daughters father all the sudden wants to see her: Thoughts?

Ok, my daughter is 5yrs old now. Her “SPERM DONOR” has not seen her since she was eight months old. He isn’t on the birth certificate. The ONLY father she knows is who has raised her since she just turned 2. Now out of the blue, he wants to start a “bond” with her and take her out and all this… She has no clue who he is, and I know if I just let her go, she’d feel so scared with a stranger. I’ve invited him to her birthday party each yr, and he’s NEVER showed. Again he’s a complete stranger to her… What would u guys personally do? No child support is in order. He wants to stay out of the court system. I just have so many mixed feelings right now… Idk how to explain this to her so a 5 yr old would understand all this…