Transport for London (TfL) knows what kind of crowds descend upon the city at the time of a royal wedding, and it’s doing its part by offering a limited-edition Oyster farecard commemorating the April 29 marriage of Prince William to Catherine Middleton. TfL will make the cards available beginning April 21.

Around 750,000 of the cards will be sold from all London Underground and London Overground stations. They will have the same charge as the regular Oyster: £5 deposit and at least £5 in fares.

“Just as royal wedding fever starts to take hold in the city, this fantastic commemorative Oyster card is a great chance for Londoners and visitors to have a slice of the action as a fabulous memento of the happy day,” the mayor said.

 “London’s transport network will play a key role in helping people travel to the wedding celebrations, so it is appropriate that we commemorate the day with a limited-edition Oyster card,” added London Transport Commissioner Peter Hendy.

TfL is following precedent with the issuance of a commemorative farecard. In 1981, the agency’s predecessor, London Transport, produced a unique £2 ticket in honor of the marriage of William’s parents, Charles and Diana.