An accounting question - on goodwill after transfer of ownership

Hi all long time lurker, first time poster. I'm working on a company that the ownership of the company is set to change hands. Owner bought private company A at USD100, and sells it at USD200. With the new ownership, I understand that there is a premium of 100 to be book, supposedly goodwill.

Can someone walk through the high level mechanics of how that works? Essentially, I thought the original owner walks away with 100 in his pocket, but Im told that is not the case. Thanks