Clearly is her dad :3 Can't be an older brother. Shining Armor looked younger than his current adult colt self when Twilight was the age Dash is in this flashback, which means that has to be her dad.

I wonder who the mother is. Since Celestia is the only other pony with a rainbow mane, my non-serious head canon is that Dashie is a princess to be as well, and will overthrow Twilight as Best Princess.

Since Celestia is the only other pony with a rainbow mane, my non-serious head canon is that Dashie is a princess to be as well, and will overthrow Twilight as Best Princess.

Soooooo Dash's dad bucked Celestia?! =O

Soooooo Dash's dad bucked Celestia?! =O

Celestia's over 2000 years old. I'm sure she likes to have a fling every now and then with some cute colt.

He is new best stallion. Find another job Soarin'

I bet her mom looks great, too bad she might not appear yet

I bet her mom looks great, too bad she might not appear yet

Ooooh I didn't think of that! Now I wanna know what her mom looks like >.>

Gasp! Dashie's Dad? Wow.

ok if we see her mom and she has a rainbow mane too...... would that point towards RD being inbred?

AAHHHHHH SNAP!

I really, really was not expecting this.  

He is new best stallion. Find another job Soarin'   I bet her mom looks great, too bad she might not appear yet

Maybe she was raised solely by him?  Would explain her tomboyish nature.

WOW.

NICE JOB PUTTING THE SPOILER ALERT IN THERE, I COULDN'T SEE THE HUGE SPOILER AT ALL.

I expected, the mother to have the rainbow mane.... O_o

That definetely looks like rainbowdash's father.But what about her mother?

Eww.

Seriously, looks like a really bad OC.

Clearly is her dad :3 Can't be an older brother. Shining Armor looked younger than his current adult colt self when Twilight was the age Dash is in this flashback, which means that has to be her dad.

 

I wonder who the mother is. Since Celestia is the only other pony with a rainbow mane, my non-serious head canon is that Dashie is a princess to be as well, and will overthrow Twilight as Best Princess.

Well actually you only compared the age difference between shining armor and twilight with rainbow dash and supposedly her 'dad'. We can safely assume that rainbow dash was the same age as Applebloom back when you see rainbow dash with her relative 'dad'. Now compare the age difference with Applebloom and Big mac. Big mac looks to be a full grown stallion and appears to be the same age as rainbow dash's dad. Now i'm not convinced that he is rainbow dash's dad, it could still be her brother if you include all the evidence of the age difference so as apposed to your statement 'clearly' is not the correct term to be used here. Only time can tell if he is her brother or farther but its still very possible if it is her brother.