According to a statement by the Labour party

Uh oh, it looks like it's not just May that is going to have a sit-down with European leaders at the summit today. Labour party leader, Jeremy Corbyn, is also now reportedly heading over as well.

This should be interesting. Corbyn is scheduled to meet with Michel Barnier, Martin Selmayr, two EU commissioners and seven EU prime ministers. The meetings reportedly will take place just before the European Council meeting.