The airport said the move was "not entirely unexpected."
There had been a commitment by International Airlines Group (IAG) to free up Gatwick slots used for Belfast and Dublin services as part of its takeover of the Irish carrier.
Ryanair is among the other airlines hoping to step in.
Any new Ryanair service would, however, likely be operated from Belfast International and there have been discussions between the parties.
Belfast International said it had no comment to make.
Belfast International Airport could be about to land Ryanair for the first time.
Perhaps a more intriguing question is would a Gatwick service be the start of something bigger?
Easyjet is, of course, a major presence at Aldergove.
Insiders often say the carriers are loathe to compete on the same routes from the one airport.
It is no secret the International has been courting Ryanair.
Talks have taken place but nothing is signed and sealed.
The length of the runway saw Ryanair pull out of George Best Belfast City Airport years ago.
Nothing has changed on that front - leaving the International as the option.
Ryanair does, of course, also run services from City of Derry Airport.
Aer Lingus will discontinue its Belfast City-Gatwick route from March 27, with suggestions it was performing poorly.
It apologised to customers who have existing bookings after that date, saying they would be offered alternative options or a refund.
A spokesperson for George Best Belfast City Airport said: "The continuing commitment by Aer Lingus to Belfast City is clear."
They said the airline is increasing capacity on flights between the City and Heathrow by using larger aircraft.
Aer Lingus is to end flights between George Best Belfast City Airport and London Gatwick from March next year.