@Masem  
Eeyup. It was just confirmed. He spend sll those years in the Umbrum’s prison waiting the moment to come out.

@Vree  
I have a feeling that based on the start of issue #2 of the Siege that time moves differently in the Umbrum world, so its a time skip for her.

@Masem  
that was an excellent summary! just two more things:
 
It was Hope who called in the two princesses to take down Sombra after he destroyed the old queen and took over the place and made the crystal ponies slaves.  
Sombra intentionally left Hope outside when he took the empire with him 1000 years into the future after his defeat by the two princesses, intended as a poetic revenge for her betrayal (Hope would be the only crystal pony left and she would have to contemplate on that fate alone).
 
I don’t think it’s been covered how she goes on to live with the umbrum, speak with her imaginary friends and somehow survive for 1000 years in released isues yet.

@Sparkler  
In Fiendship #1, we learn that the Umbrum appeared to have created Sombra as an otherwise ordinary unicorn stallion as to infiltrate the Crystal Empire to steal the Crystal Heart which kept them at bay. He came to as a colt with apparent amnesia and was taken in to a orphanage.
 
Radiant Hope quickly befriended him as she herself was strange (she kept going on about her imaginary friends) and ostracized by the other ponies there. As they grew up, the Crystal Heart would prevent Sombra from going to the Crystal Faire, and Radiant stayed by his side. At point point, Sombra literally started falling to pieces from the Heart, and Radiant used powerful magic to keep him together, which got herseld that cutie mark, a unicorn with magic to heal almost anything.
 
This caused Sombra to fear an earlier fate he saw in the Crystal HEart, fled the city, and discovered the Umbrum and his true identity. Becoming evil, he went to steal the Heart, turned Princess Amore to crystal and shattered her, all in from of Radiant who still felt there was good in Sombra. Radiant ran off before Sombra sealed the Empire for 1000 yr.

@Psyga315  

 
Well, it is obvious that Celestia won’t blast off her head with a shotgun or Luna won’t chop it in half with an axe…

@soundtea  

 
Well, we all tend to be idiots at times where individuals we care about are concerned. Maybe not to the extent of “helping evil king reclaim/enslave his former empire”, but that’s a pretty specific circumstance really. Besides, they have a history together. It’s hard sometimes to look at someone you remember from the halcyon days of youth and reconcile that with what they’ve ultimately become.
 
And hey, even overlooking all that, maybe she’ll even be the one to bring him down. She’d be the one he’d least suspect, after all.

@Psyga315  
Yah, “ destiny” right? That’s why he chose to be evil right? Sorry, as a wise old knight once said, “he chose, poorly”.

@Sparkler  
Well, from what I know, Hope went to find a way to save Sombra from being the generic evil person we barely get a focus on in “MERCHANDISING: THE TWO PARTER #2” and she ended up in a land full of cute puff demons that Kyubey from Madoka would call deceiving pricks.
 
She goes and rallies up a bunch of villains, and by villains I mean the one actual villain, a couple of jerks, and an actual nice guy who went through some bullshit desire of “wanting people to fear him” to raid the Crystal Playset and free Sombra.
 
And he is free. And pretty much kicked everyone’s ass to the point where anyone ‘‘sane’’ would get that freeing an evil monster is a ‘‘bad’’ thing. Even ‘‘if’’ he was your friend.
 
I’m really waiting for Hope to lay the verbal smackdown on Celestia for how “destiny” ruined Sombra’s life

Could someone fill me in on Radiant Hope?

Yeah, Hope’s a pretty big idiot.
 
20 bucks is that she gets IDW’s trademark express forgivness.