The Brothers Black
This is one of my more ridiculus Harry Potter theories, though I think you will find that it makes an amazing amount of sense. Sirius and Regulus are brothers. Sirius is the older of the two, and the Harry Potter fandom has always made a (logical) assumption that there is a year difference between the two. Who is to say that there is even that much of a difference between the two brothers though? Perhaps the age difference is something more like a minute. Yes, I am suggesting that Sirius and Regulus are twins.
JKR never specifies the age difference between Regulus and Sirius. For practical reasons, it has always been assumed that Regulus is a year younger because JKR does say is that Sirius is older and that Regulus was a Death Eater. A year, maybe two (if Regulus had joined the Death Eater ranks before he graduated), is the largest gap there could be between the brothers. However, the age gap could also be smaller than we are supposing. Here's why:
First, the longer Regulus has been a death eater the longer he would have to get in too deep and start backing out. Particularly if he is the mysterious R.A.B. (notice the "particularly;" I am not trying to begin a RAB debate), JKR would need as much time as she could muster for Regulus to get close enough to the Dark Lord to see that he is doing something very wrong, even for a Dark Lord. A turn around of only a year (which would be the case if Regulus joined up with the Death Eaters when he graduated Hogwarts in 1979 and then died in 1980) would not be a convincing time slot for all of this to happen. If he graduated in 1978, however, with Sirius, he would have two years to see the error in his ways. For me, this seems like an appropriate amount of time for all of this to occur. He has time to get in with the Voldie (remember, this would happen faster for Regulus because he is related to Bellatrix LeStrange and the Malfoys), be happy about being a Death Eater, and then freak out.
This last point is not what convinced me. It is merely what got me started thinking about the possibility. Mrs. Black's age is a much larger clue in this mystery. Mrs. Black is described as being very old, to the point where Sirius would have been a late-life gift. Are we suddenly to believe that a very old woman, barren up until this point, is suddenly impregnated twice? The second time occuring only a year after the first? The odds are not good. If Mrs. Black was unable to concieve for all of those years (and she was trying; she was a pure-blood woman whose only job was to keep the Black bloodline alive), then why is it going to happen twice in a row now? Because it didn't. Sirius and Regulus came in the same package. Sirius is noted as the oldest because of pureblood inheritance traditions. The oldest child inherits the family name, money, and house (as we saw with the confusion over the ownership of Number 12 Grimmauld Place). It is not split between two people.
Furthermore, Sirius cares about what happened to his brother. Sirius is not able to just forget about him and not care as he does with the rest of his family. Sirius inquires into what happened to Regulus, and though he might not respect his brother, he cares about what happened to him. Why is this? Twins are noted for sharing a special bond (whether they actually do or not is unimportant; what is important is that JKR might recognize this in her world of wizardry). Sirius might hate his twin, but he cannot overlook him as he would Narcissa's whining over Draco's mission.
Why wouldn't Sirius tell Harry he had a twin? Quite simply. Would you tell your godson that your twin was a Death Eater? Paricularly if your godson was Harry. Harry's only experience with twins is the Weasleys. Fred and George are so much alike, their own mother can hardly tell them apart. Telling Harry Regulus was Sirius's twin would discredit Sirius in Harry's eyes, even if Harry did not do so intentionally. Furthermore, Sirius might not want to admit what happened to his brother, his twin, himself. Therefore, he describes Regulus as being his younger brother, which he is, just not by much.
Last, Sirius, the star for which our favorite reckless convict is named, is a binary star. Meaning, there are two stars making up Sirius. There are several dog constellations which JKR could have used to foreshadow our favorite reckless convict's animagus form, so why would JKR pick this one in particular? Because it is a binary star. Not only would JKR foreshadow Sirius's animagus form, but she would also be foreshadowing the existence of a twin. Regulus is not a binary star, but it does act as one. It's written in the stars, for Merlin's sake, and, no matter what Dumbledore says, the stars are usually right if we interpret them correctly.
JKR never specifies the age difference between Regulus and Sirius. For practical reasons, it has always been assumed that Regulus is a year younger because JKR does say is that Sirius is older and that Regulus was a Death Eater. A year, maybe two (if Regulus had joined the Death Eater ranks before he graduated), is the largest gap there could be between the brothers. However, the age gap could also be smaller than we are supposing. Here's why:
First, the longer Regulus has been a death eater the longer he would have to get in too deep and start backing out. Particularly if he is the mysterious R.A.B. (notice the "particularly;" I am not trying to begin a RAB debate), JKR would need as much time as she could muster for Regulus to get close enough to the Dark Lord to see that he is doing something very wrong, even for a Dark Lord. A turn around of only a year (which would be the case if Regulus joined up with the Death Eaters when he graduated Hogwarts in 1979 and then died in 1980) would not be a convincing time slot for all of this to happen. If he graduated in 1978, however, with Sirius, he would have two years to see the error in his ways. For me, this seems like an appropriate amount of time for all of this to occur. He has time to get in with the Voldie (remember, this would happen faster for Regulus because he is related to Bellatrix LeStrange and the Malfoys), be happy about being a Death Eater, and then freak out.
This last point is not what convinced me. It is merely what got me started thinking about the possibility. Mrs. Black's age is a much larger clue in this mystery. Mrs. Black is described as being very old, to the point where Sirius would have been a late-life gift. Are we suddenly to believe that a very old woman, barren up until this point, is suddenly impregnated twice? The second time occuring only a year after the first? The odds are not good. If Mrs. Black was unable to concieve for all of those years (and she was trying; she was a pure-blood woman whose only job was to keep the Black bloodline alive), then why is it going to happen twice in a row now? Because it didn't. Sirius and Regulus came in the same package. Sirius is noted as the oldest because of pureblood inheritance traditions. The oldest child inherits the family name, money, and house (as we saw with the confusion over the ownership of Number 12 Grimmauld Place). It is not split between two people.
Furthermore, Sirius cares about what happened to his brother. Sirius is not able to just forget about him and not care as he does with the rest of his family. Sirius inquires into what happened to Regulus, and though he might not respect his brother, he cares about what happened to him. Why is this? Twins are noted for sharing a special bond (whether they actually do or not is unimportant; what is important is that JKR might recognize this in her world of wizardry). Sirius might hate his twin, but he cannot overlook him as he would Narcissa's whining over Draco's mission.
Why wouldn't Sirius tell Harry he had a twin? Quite simply. Would you tell your godson that your twin was a Death Eater? Paricularly if your godson was Harry. Harry's only experience with twins is the Weasleys. Fred and George are so much alike, their own mother can hardly tell them apart. Telling Harry Regulus was Sirius's twin would discredit Sirius in Harry's eyes, even if Harry did not do so intentionally. Furthermore, Sirius might not want to admit what happened to his brother, his twin, himself. Therefore, he describes Regulus as being his younger brother, which he is, just not by much.
Last, Sirius, the star for which our favorite reckless convict is named, is a binary star. Meaning, there are two stars making up Sirius. There are several dog constellations which JKR could have used to foreshadow our favorite reckless convict's animagus form, so why would JKR pick this one in particular? Because it is a binary star. Not only would JKR foreshadow Sirius's animagus form, but she would also be foreshadowing the existence of a twin. Regulus is not a binary star, but it does act as one. It's written in the stars, for Merlin's sake, and, no matter what Dumbledore says, the stars are usually right if we interpret them correctly.