Portsmouth have confirmed that a fan died during their friendly against local rivals Bournemouth on Saturday.
The supporter was taken ill during Pompey's 2-1 defeat to the Cherries and was unable to be revived after being taken to hospital.
The League One club released a statement on Saturday night, offering their condolences to the supporter's family.
It read: "Portsmouth Football Club are sad to announce that a Pompey fan has passed away after falling ill at today's match.
"The incident occurred during the half-time break and the start of the second half was delayed while he received treatment.
"Despite valiant attempts by medical staff - who were quickly on hand to administer CPR - and following transportation to QA Hospital, he was unable to be revived.
"Next of kin have been notified and our thoughts are with them at this time."
Bournemouth defender Nathan Ake and Portsmouth winger Conor Chaplin also offered their condolences via Twitter.