Alun Wyn Jones, 38, said it was picked up in the summer by a club doctor at French side Toulon, where he ended his playing career last month.

Jones said he would be forever grateful to Toulon, adding: "Had they not offered me a contract, I may never have known about the heart condition."

Atrial fibrillation "causes an irregular and often abnormally fast heart rate" and can lead to problems including dizziness, shortness of breath and tiredness, according to the NHS.

Jones told The Telegraph his condition "was discovered when I underwent a full medical check, which included an ECG test, when I joined Toulon in July on a short-term contract as cover during the World Cup".

"The cardiac doctor picked it up straight away. My heartbeat was like a galloping horse with six legs. It was all over the shop.

"The things that bring it on for someone my age is likely to be cardiovascular exercise and stress, it occurs in sports like rowing and endurance sports, but it was a shock because throughout my career I have always prided myself on my fitness.

"I have always been so committed to doing extras after matches, constantly working on my fitness and recovery from injuries."

Jones announced his retirement from international rugby in May.

He eventually quit the sport in November, before having surgery on his heart that same month.

Jones said he hopes more players can have heart screenings, so they can discover any issues.

The Welshman told The Telegraph: "There is a lot of talk about welfare in rugby at the minute, but does that cover everything?

"Is it just things that we can afford? Surely the sport has come on to the point where players should be screened more often, especially at a time when the demands in the game are growing.

"I was very lucky how it worked out and will forever be grateful to Toulon for signing me."

Jones is the most capped player in rugby union after making 158 appearances for Wales and 12 for the British and Irish Lions.

Read more: Gavin Henson and Phil Vickery among over 200 ex-rugby stars taking legal action over brain injuries

Jones's comments come weeks after a number of former players began legal action over brain injuries against the English Rugby Football Union (RFU), Welsh Rugby Union (WRU) and World Rugby.

English World Cup winner Steve Thompson is among those suing rugby authorities, and said he had been diagnosed with early onset dementia as a result of his playing career.