When we remove the strum from this pattern, the initial instinct will be to to stop the strumming motion in your picking hand. This is exactly what we DON'T want, as this alters the on-beat downstrum / off-beat upstrum pattern we've established.
The key to this playing this strum successfully is to keep the strumming motion going while slightly lifting the hand away from the body of the guitar momentarily, on the downstroke of the third beat, so the pick misses the strings. Then, on the next upstroke (the "and" of the third beat), bring the hand closer to the guitar, so the pick hits the strings. To summarize: the upward/downward motion of the picking hand should not change from the first pattern. Deliberately avoiding the strings with the pick on the third beat of the pattern is the only change.
Listen to, and play along with, this second strumming pattern, to get a better idea on how this new pattern should sound. Once you are comfortable with this, try it at a somewhat faster speed. It is important to be able to play this accurately - don't be satisfied with getting MOST of the up and down strums in the right order. If it's not perfect, it will make learning any harder strums virtually impossible. Be sure that you can play the pattern many times in a row, without having to stop because of an incorrect strum.
This is a tricky concept, and it can be guaranteed that you will have some problems with it at first. The idea is, if you introduce basic strumming patterns early, within a couple of lessons, you'll have gotten the hang of it, and will be sounding great! It is important to try not to get frustrated... soon, this will become second nature.