Former UFC double-champion Conor McGregor paid tribute to Irish singer Sinead O'Connor.

O'Connor passed away at the age of 56 on Wednesday. Her family announced her death without revealing the cause or any further details.

“It is with great sadness that we announce the passing of our beloved Sinead,” the statement read. “Her family and friends are devastated and have requested privacy at this very difficult time.”

The 90's pop star was perhaps most well known for her No. 1 hit Nothing Compares 2 U while she also made a number of headlines for tearing up a picture of Pope John Paul II while performing on Saturday Night Live back in 1992.

However, UFC fans will know her best as the singer of McGregor's Foggy Dew walkout song.

O'Connor even performed a rendition of the song during McGregor's walkout against Chad Mendes at UFC 189 back in July 2015.

And so, Conor McGregor took to Twitter to not only pay tribute to one of Ireland's most iconic singers, but also to a friend.

“The world has lost an artist with the voice of an Angel,” McGregor wrote. “Ireland has lost an iconic voice and one of our absolute finest, by a long shot. And I have lost a friend. Sinead’s music will live on and continue to inspire! Rest In Peace, Sinead you are home with your son I am sure.”

O'Connor is survived by three children. Her son Shane tragically died at the age of 17 last year.

You can watch her performance of Foggy Dew at UFC 189 below: