What is the ruling on someone who forgot to perform ghusl after janabah while fasting in Ramadan and remembered it after breaking their fast?

Being in a state of ritual impurity (janabah) does not affect the validity of the fast. The fast of one in a state of janabah is valid, whether he intentionally delayed ghusl (ritual bath) or forgot it. This is because it is established that the Prophet, peace and blessings be upon him, would wake up in a state of janabah and then fast. However, one who is in a state of janabah must make up all the prayers he performed after becoming جنبا and before performing ghusl.