My DD1 has a similar situation.
I split from XH when DD1 was a few months old.
Met DH when she was 11mths old.
DH moved in with us 6mths later and DD started calling him daddy all on her own.
She saw XH once or twice a month and also called him dad.
She has grown up knowing she has 2 dads and we've always reinforced that to her.
If you keep reinforcing the same thins to her without differing she will soon know it for herself.