While it wasn’t a secret, I just learned last week that Trader Joe’s is owned by Aldi (some information here).  I read that in the context of Walmart giving up in Germany.  This actually happened back in 1976, so it surprises me that I didn’t hear about that sooner.  I never saw Aldi-branded products at TJs, but Aldi in Germany is carrying Trader Joe’s products (i.e. nuts).