Heir Hunting Contract

[Jasper65]

I undertook an Heir Hunting case some years ago and was paid my fee as a percentage of the clients share. I made my client aware other Heirs may be likely to come forward for a share. I did not do the administration. And my signed contract states that if anyone else claims on the estate at a later date that it is his concern and not mine. Contract also states our commitment to each other ends at that point. Now a few years later someone else has come forward and he wants me to pay back my fee as his entitlement has changed? Doesn't the guarantee he made on contract cover me now?