'What's up with Kim's face?'

She's stayed out of view for weeks since giving birth to son Saint early last month.

But Kim Kardashian made a return to the spotlight in an unexpectedly low key fashion with an appearance on sister Kourtney's Instagram feed on Sunday.

The image sparked a huge response from fans - but it wasn't her svelte post-baby body that they were surprised by.

Instead fans speculated about the reality star's face, with many suggesting that she had used her time out of the spotlight to have some work done.

'What's up with Kim's face?' wrote one commentator, while others remarked that she looked almost unrecognizable.