Complex sentence: Eve Arden was also an old friend of Desi's and his ex-wife, Lucille Ball, with whom she worked at RKO in the 1930's, but NBC had found Ann and Eve's styles of comedy too similar for the way the show was written.
Split into simpler sentences: Eve Arden was also an old friend of Arnaz and his ex-wife Lucille Ball, with whom she worked at RKO in the 1930's. However, NBC found Ann and Eve's styles of comedy too similar for the way the show was written.