On 2 March 1874 he was raised to the peerage as Baron Cottesloe, of Swanbourne and Hardwick in the County of Buckingham, in recognition of his services.

Her mother was the American born diarist Maria Nugent.

Their third son, Charles William Fremantle was the longtime Deputy Director and Comptroller of the Royal Mint.

Their fourth son Sir Edmund Robert Fremantle was an Admiral in the Royal Navy.

Lord Cottesloe survived her by fifteen years and died in December 1890, aged 92.