is it true that they are bring a new actor in to supernatural to play brother to sam and dean what they don't know about?

Yeah an actor named Jake Abel is gonna play the third Winchester brother. The episode airs April 23rd. If you google it you can find the article about it on tvguide's website I think...

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"Supernatural" will take a two-week break and a promo for the April 23 episode is available. Called "Jump the Shark", this would be the episode where a third Winchester brother is introduced. Played by Jake Abel, the character is named Adam Milligan and he is conceived while John Winchester set out on his hunting adventure and met Kate Mullany.

In the episode, Adam's life is changed after he transitions to be a monster. Creator Eric Kripke explained the addition of the third brother to TV Guide, "When we were breaking the story about the third Winchester brother, we knew the fans would scream that we had jumped the shark. Of course, adding a new sibling or relative to an established series is a classic and cherished shark jump, Cousin Oliver being the patron saint of the practice (Brady Bunch)."

He continued, "For fans who are worried that we are truly jumping the shark... watch the episode, decide for yourself. Personally, I don't think we're gassing up the motorcycle quite yet, but you tell me." "
OMG I Cannot Believe IT!!!
What?!Does He Ride In the Turnk Or In the Back Seat?Where Dean Throws His Packets?L.o.l That ll Be Funny...

i heard this but i really hope they dont because personally i think it will ruin it, thats just my opinion though.

yes they brought in adam, a younger brother

Adam has been on the show, before. If you remember him and his mother had been killed and replaced as monsters. Then at the end of the 5th season adam once again appeared again and was fighting with sam and was falling into hell with sam. I am not to much in favor of another brother. These brothers have been through way to much.