The former couple, who dated for two years between 2012-2014, arrived separately to the event.
Two two ended their relationship amicably, so we assume the old flames would have enjoyed catching up!
Cressida and Harry weren't the only ones in attendance - Pippa and Carol Middleton, the sister and mother of Harry's sister-in-law Kate Middleton - were also in attendance.
With Prince Harry officially off the market, we took a look back at his dating history. If you want to see all the women Harry has dated in the past, see here.