Tchaikovskij's Swan Lake and Wagner's Lohengrin

Now last weekend I saw Lohengrin on the (swedish) Royal Opera. I thought I heard a theme in Lohengrin, probably Elsa's theme, which I think figures in Tchaikovsij's Swan Lake.

Is there any special stories behind this? I mean, Lohengrin is the swan knight, so the connection could be there?