Robert Francis St Clair-Erskine, 4th Earl of Rosslyn (2 March 1833 – 6 September 1890),[1] styled Lord Loughborough from 1851 until 1866, was a British Conservative politician.

He served under Lord Salisbury as Captain of the Honourable Corps of Gentlemen-at-Arms from 1886 until shortly before his death in September 1890.

They had five children: Lady Rosslyn had two daughters by her first marriage: Frances Evelyn "Daisy" Maynard (who married Francis Greville, 5th Earl of Warwick) and Blanche "Blanchie" Maynard (who married Lord Algernon Gordon-Lennox and was the mother of Ivy Cavendish-Bentinck, Duchess of Portland).

Lady Rosslyn survived her husband by over 40 years and died at York Terrace, Regent's Park, London, in December 1933.

She knew personally many of the most famous people of the Victorian era, including Benjamin Disraeli and William Gladstone.