Cooper was renowned for her steamy fiction, including novels like Riders and Rivals, which explored scandal and adultery in upper-class society.
Her novel Rivals was recently adapted into a hit Disney+ series, starring actors such as Danny Dyer and David Tennant.
Tributes were paid by the showrunners of 'Rivals', her children Felix and Emily, and the Queen, who described her as a 'legend' and a 'wonderfully witty and compassionate friend'.