Walter Buckler Lethbridge was a barrister. He did not marry. He had an older sister Maria (b. ca 1822) and a cousin Maria (b. ca. 1830).
Lethbridge was possibly a partner in the firm of solicitors Lethbridge & Prior of 25 Abingdon Street, London. However, by 1881 he was no longer in practice and lived at 71 Portland Place. During this year he made a trip to Venice and JW gave him advice about where best to stay (#10689).
Around 1884 Lethbridge appears to have bought a portrait from JW. This may have been a portrait of himself but there is no record of such a painting having been made (#10690). He was among those on JW's guest list for the private viewing of the Royal Society of British Artists' 1887-88 winter exhibition (#13403). He was also invited to a dinner at the Criterion, Piccadilly, on 1 May 1889, organised by W. C. Symons to congratulate JW on being made an honorary member of the Royal Academy in Munich, but he had to decline (#02516).
UK census 1881, from http://www.familysearch.org (accessed 2004); The Mayfair etc Directory, 1886-87.