The ugli fruit is a cross between a grapefruit, an orange and which other fruit?

The ugli fruit is a Jamaican form of tangelo, a citrus fruit created by hybridizing a grapefruit (or pomelo), an orange, and a tangerine.

Ugli was discovered growing wild (possibly having developed in the same way grapefruit was created) in Jamaica, where it is mainly grown today. The name is a variation of the word "ugly", which refers to the fruit's unsightly appearance, with rough, wrinkled, greenish-yellow rind, wrapped loosely around the orange pulpy citrus inside. UGLI is a registered trademark of Cabel Hall Citrus Limited, under which it markets the fruit.

The light-green surface blemishes turn orange when the fruit is at its peak ripeness. An ugli fruit is usually slightly larger than a grapefruit (but this varies) and has fewer seeds. The flesh is very juicy and tends towards the sweet side of the tangerine rather than the bitter side of its grapefruit lineage, with a fragrant rind.