Olympic swimming hero Michael Phelps reportedly spent eight hours gambling in a casino in Baltimore, Maryland before getting arrested and charged with drink-driving.

The 22-time Olympic medallist was pulled over by police in his home state when he was allegedly caught speeding at 84mph in a 45mph zone in the early hours of Tuesday morning.

According to TMZ, the arrest happened shortly after Phelps left the Horseshoe Casino at around 1am after spending eight hours in a private VIP gambling room.

The report claims that the 29-year-old, who is known to be a fan of poker, was drinking beer while playing blackjack.

Phelps took to Twitter to on Tuesday to apologise for the drink-driving charge.