'Isabella' was one of the first paintings made in the new Pre-Raphaelite style. It was begun shortly after the founding of the Pre-Raphaelite Brotherhood in 1848, when Millais was only 19.
The subject is taken from a poem by John Keats (1795-1821), based on a story by the Italian writer Boccaccio (died 1375). It tells of the love between Isabella, the sister of wealthy Florentine merchants, and their poor apprentice Lorenzo. The jealous brothers later murder Lorenzo, but his body is found by Isabella, who cuts off his head and buries it in a pot of basil, which she waters with her tears.
The ending is hinted at in this painting by the pot of herbs in the background. There are other signs of the coming tragedy too. One of the brothers is shown aiming a kick at Isabella's dog, while the lovers share a blood orange, signifying the later spilling of Lorenzo's blood.