Serena posts heartfelt baby message on fiances birthday

I think there may be some confusion here!

Serena Williams is a professional tennis player, and I'm not aware of her posting a heartfelt baby message on her fiancé's birthday. Could you provide more context or clarify what you're referring to?

If you meant to say that Serena Williams posted a heartfelt message about her baby on her fiancé's birthday, that would be a lovely gesture!