Why has my cat been acting like this?

I’ve had my cat Ashes since he was a baby. He’s 4 now.
My sister gave us her 11 year old male cat Luke last year.
We introduced the cats to each other about 6 months ago.
They became really close, and played all of the time.
About 3 weeks ago, Luke passed away.
Ashes, who is usually independent, has picked up some of Luke’s mannerisms.
Luke was very affectionate, and would always jump up onto your shoulders and drape like a scarf. Ashes NEVER did that (literally. Not once.) until a week after Luke passed.
He also does other odd things that Luke was famous for, like sitting on the toilet seat and drinking out of the sink.
The strangest thing about all of this is….Ashes is a big fat tabby cat, and Luke was an exotic looking cat. (Looked like this. http://www.vistamania.com/kattres/images/jackson2.jpg) Luke didn’t meow, he did something that sounded like a honk. Ashes always sounded like a normal cat but recently…he started HONKING.
I’m a little bit freaked out. Can someone explain why his behavior has changed? For the most part, Ashes acts like himself but he has his moments, and everyone in my house is curious!