It's thought Homer's death was caused by a blood clot, brought about by intense sadness at the loss of his mate.
The manager of Blackpool Zoo, Iain Valentine, said orang-utans often go into a deep depression following the death of a partner.
He said Homer and Hayley were inseparable. And added that Homer even gave her a Valentine card.
However, a third ape at the zoo, Lomie, has also died within the last 48 hours, sparking fears of a deadly bug at the centre.
A vet is looking into the matter.