Dp's exW changed her name by deed poll to new boyfriends name after they split. She was pregnant and split with new boyfriend just after the birth. Baby was given dp's surname and his exW has now reverted to that name too. Baby is one million percent not dp's but I think he needs to make sure she didn't put him on the birth certificate as it could cause issues in the future. DP has done nothing about it. AIBU?