using TLS (>1.2) with more than one certificate

[Tobias.Wolf]

I've a server application and need to support RSA and ECC clients at the same 
time.
I don't know which certificate from my local keystore I have to send to the 
client, btw I have a rsa and a ecc certificate in my keystore already.
I don't know with which certificate (rsa or ecc) a client comes during 
handshake of a tls connection.
How can this technically work?