This picture takes place sometime after #8 at least. Not sure if it's still within Discovery's timespan or after. Use your imagination. I spent no effort on this page and I was actually partially inebriated from karaoking with friends when I finished coloring this. XD
That said, here's a little snippet on how they met:
"Who art thou to have entered the lair of the Moon Princess?!"
"Oh, sparks! Oh, s-sparks, nooooo!"
"SPEAK, giant, metallic creature or we shall be swift and brutal!"
"NO! NO BRUTAL!"
"Does thou prefer slow and brutal?"
"I don't prefer any kind of brutal! Please don't kill me! I already got shot out of a cannon by the other ponies! I mean you no harm!"
"Be you the vile creature that plagued the village of Ponyville and caused grievous on our people?"
"It was an ACCIDENT! *cries*"
"...Frightened. Y-You are frightened."
"Well, OF COURSE! Everyone thinks I'm the bad guy! I never asked for this! I don't want this! Is it because I'm Decepticon? Is it because I'm black and purple and all these dark colors?!"
"...We...er...I understand. I was once a terrible princess myself. My sister, the Goddess of the Sun, banished me for a thousand years and I am still repenting for my sins."
"T-That's horrible, Miss...er..."
"I am Princess Luna."
"A pleasure. Please, you may stop kneeling; I shall perform no acts of torment. I simple wish to talk."
"It can get quite lonely up in the moon. And I personally feel we have quite a bit in common."
"Yeah. Talk. Okay. That sounds good. We can do that. The talking, that is."
"So tell me of yourself. You are quite a strange creature."
"Oh, I'm Cybertronian. Although if you want another thing in common, technically, I was born on a moon. I'm part of the Decepticon faction; my symbol is this. A lot of my kind hates that symbol. I don't like it either."
"Perhaps you can remove it and replace it with another."
"Remove...huh, that's an idea. I got to keep that in mind."
"How did you came to be?"
"Oh, well, this is going to sound weird, but I'm really one of a series of clones to a really jerky, evil, spiteful bot named Starscream..."
And the rest is history...