its been discussed sooooo much everywhere .... and its very accurate too .. specially with the "heavy locket none of them could open" in the 5th book when they are cleaning 12 grimmuald place ..... but its just not possible that jk rowling will have it that predictable .... she usually has stuff that no one can even guess ... like in the third book sirius being good and oeter pettigrew bad ....... and in 4th book .. who woulda thought of alastor moody
and in the 6th book about the half-blood prince .... i can bet most of the people like me thought of the half-blood prince being voldemort ... since he was half-blood and he lived 50 years ago and that was the date on the book :)
so its supposed to be tricky i guess ... but you cant help thinking its regulus black ..... so its really complicated :)
maybe jk rowling panicked by thinking how many people have guessed it right and actually changed the person who should be RAB 😆