if lady florence was a cousin of queen victoria the relationship must be very distant as i have not found any trevelyan cousins amomgst the legimate or illegimate descendants of king george III , frederick prince of wales nor king george II !!
It appears the claim is that Mary Wilson, the grandmother, was a cousin of Queen Victoria, but so far I have found no evidence of a relationship either.
I can say several things about the claims put forward on the websites mentioning Florence Trevelyan, however.
The first is that "Lady" Florence Trevelyan was never eligible to hold a title.. not even by courtesy. Her father, Edward Spencer Trevelyan, was a younger son of Sir John Trevelyan, 5th Baronet Trevelyan of Nettlecomb, Dorset, and his wife Mary Wilson.
Mary Wilson's father was Sir Thomas Spencer Wilson, 6th Baronet Wilson
(later Maryon-Wilson) of Eastbourne, Sussex. Her mother was Jane Weller, a daughter of John Weller and Margaretta Peers. Mary Wilson was sometimes referred to as Maria. One thing is certain.. and that is Mary Wilson was
not a first cousin of Queen Victoria.
Florence Trevelyan's mother was Catherine Anne Forster, a daughter of John Forster and Rebecca Bell. I don't believe her father held any title.
I have found no evidence in any of Florence's known ancestral lines to show a connection or relationship to the royal family. Nor do I find anyone named Trevelyan in the list of Queen Victoria's attendants. One website mentioned that either a cousin or an aunt of Florence was a lady-in-waiting, which is false as far as I can tell.
There was only one Baron Trevelyan. He was Sir Humphrey Trevelyan, KG, created a Baron on 12 February 1968. The peerage became extinct on his death in February 1985. I do not know if Humphrey is from the same family, but there is probably some connection.
To say that Florence was a descendant of the "Lords" or "Barons" Trevelyan is erroneous. Though she was a descendant of the Baronets.. either way, she was never "Lady Florence", although this could be a title she adopted in Italy to enhance her social standing.. or to secure a marriage to a wealthy Italian, as her husband appears to have been.
The Baronetage of Trevelyan of Nettlecomb, Dorset, still exists in the Trevelyan family. The current baronet is Sir Edward Norman Trevelyan, 11th Bart., who inherited the title in January 1996.
The Baronetage of Maryon-Wilson of Eastbourne, Sussex, became extinct on the death of Sir Hubert Guy Maryon-Wilson, 13th Bart., on 13 September 1978.
Who knows if the story of her affair with the Prince of Wales is true or not.. personally, I don't think it ever happened.. otherwise we would know about Florence Trevelyan, which we don't.. as a relation of Victoria - or as a mistress of Edward.
By the time she supposedly was asked to leave England in 1879, both of her parents were deceased, and she was their only surviving child. So basically, I think she could have made up any story she wanted once she was in Italy.. for whatever reason.
I hope anyone that uncovers more about this topic will post it here.
: - I grew up thinking she was a frumpy, old, and bitter widow. Sounds like she had a hard life - reminds me of some of my relatives. Ugh, being a woman back then. Thanks. 
