Ireland and Ulster captain Rory Best will retire after this year's World Cup in Japan.
The hooker, 36, made his international debut in 2005 and his tally of 117 caps is the third highest for Ireland.
"It is with mixed feelings that I announce my retirement from Ulster Rugby as of the end of this season," said Best.
"This feels like the right time for me to go out on my terms, a luxury for which I feel very privileged."
The World Cup runs from 20 September until 2 November.
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Since succeeding Paul O'Connell as captain in 2013, Best led Ireland to three Six Nations titles, including the Grand Slam in 2018.
A win over New Zealand last November capped a remarkable year for Irish rugby, although Joe Schmidt's side suffered a disappointing 2019 Six Nations and fell to heavy defeats by England and Wales.
Best has featured in three World Cups and twice been selected for the British and Irish Lions, although he did not play a Test.
Ireland, who have never reached the semi-finals of a World Cup, begin their Pool A campaign against Scotland on 22 September.
Best said: "I am very excited for the end of the season with Ulster and for the upcoming World Cup with Ireland - both of which I hope to finish with a massive high, playing at the top of my game."
In March, Best indicated that he would quit international rugby after the World Cup, although there were suggestions that he may continue his club career.
He is currently sidelined with an ankle injury suffered during Ulster's European Champions Cup quarter-final defeat by Leinster on 30 March.
He is unlikely to recover in time for the Pro14 home quarter-final, scheduled for 3/4 May, but is expected to be fit for a potential semi.