The parent "proto-planet" existed billions of years ago before breaking up in a collision and would have been about as large as Mercury or Mars.
A team has published their results in the journal Nature Communications.
They argue that the pressures necessary to produce diamonds of this kind could only occur in planet of this size.
Using high-definition microscopy, the researchers measured the composition of diamonds locked up in rocks left scattered in the Nubian desert of northern Sudan after the asteroid 2008 TC3 hit the atmosphere.
The measurements provide "the first compelling evidence for such a large body that has since disappeared", the research team write in their paper.
The finding also boosts the theory that today's Solar System planets were forged from the remains of tens of large "proto-planets".
The meteorites from this collision fall into a category of space rocks called ureilites, which account for less than 1% of objects that collide with Earth.
The researchers suggest all ureilite asteroids may be remnants of the same proto-planet.
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