Mixed relay has been officially added to the schedule for the 2015 World Aquatics Championships as Kazan gets set to host the event this summer.
It has also featured in both editions of the Summer Youth Olympic Games, in Singapore and Nanjing respectively.
The discipline was left out of the earlier schedule, released by the International Swimming Federation (FINA) in August, as organisers continued to ponder over the appropriate dates and times for the event.
The two relays that have now been added are the mixed 4x100 metres medley relay and the mixed 4x100m freestyle relay.
The medley relay falls on the fourth day of competition with the freestyle relay being contested on the seventh.
Both events will be the final races of the day, giving athletes the opportunity to focus on their individual events, if needs be.
The release of the schedule comes as Kazan celebrated the 200 Days To Go mark ahead of the World Championships, which are due to take place take place between July 24 and August 9.
To mark the occasion, the crew of the International Space Station (ISS) offered a congratulatory message to fans of the upcoming event.
Dressed in branded Kazan 2015 clothing, the three Russians on board the ISS, Alexander Samokutyaev, Elena Serova and Anton Shkaplerov, took time away from their research to look ahead to the Championships.
"Our country has kicked off a series of major international sporting events - we've already hosted the best Summer Universiade [at Kazan in 2013] and fantastic Olympic Games [in Sochi]," they said.
"There are just several months left before the FINA World Championships, which is yet another mega sporting event.
"We are pleased to also make our own contribution to the preparation of the upcoming event and to remind once again that the symbol of the 16th FINA World Championships is here with us in space.
"Busy and important days of preparation lie ahead and we wish the Championships organisers to complete their task without strain and strictly according to plan.
"As for athletes who are currently gearing for the Championships at all corners of the globe, we would like to wish them to reach their peak form so that these competitions will be not only the most well-organised but also most dramatic and action-packed!"
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December 2014: Exclusive: Mixed gender diving and synchronised swimming to take place at Kazan 2015
November 2014: FINA to introduce mixed gender events in diving and synchronised swimming
July 2013: Mixed relays to be introduced at World Swimming Championships