The Secret Worlds Legends Twitter has been updated with this post, "As a thank-you for your support in TSW, you are invited to a head start of Secret World Legends beginning on June 23rd". After reaching out to Funcom, we now know that "this is for previous The Secret World players and those who signed up for the beta (application is still open)".
We'll reach out to Funcom for clarification and keep you posted!
Source: Secret World Legends Twitter