It is claimed the Rocket Man singer, 63, and his partner David Furnish, have already been telling guests that Allen, 25, who is five months pregnant, will be performing at their annual ball.
According to UK newspaper The People, they reportedly told friends: 'We are thrilled to announce that this year our dear friend Lily Allen will give us an exclusive performance.'
The pair's relationship hasn't always been friendly as Allen fell out with Elton at a GQ awards bash two years ago and then mocked him in her music video for her single, Who'd Have Known.