Conor McGregor paid tribute to Sinéad O'Connor, who once helped the Irish MMA fighter make one of the most iconic entrances in UFC history

• Irish singer Sinéad O'Connor has died at the age of 56.
• Irish MMA fighter Conor McGregor paid tribute to the late musician.

Irish singer Sinéad O'Connor has died at the age of 56.

Many celebrities have expressed sadness and paid tribute to the late musician, and that includes Irish MMA fighter Conor McGregor.

McGregor first wrote "gutted" on Twitter in response to another tweet. The original tweet from MMA Orbit included a video of O'Connor performing the song "The Foggy Dew" during McGregor's entrance to his UFC 189 fight against Chad Mendes back in 2015.

McGregor regularly uses this song for fight entrances; however, this live version performed by O'Connor is considered by some to be "the most iconic walkout in UFC history," according to the UK Independent.

According to Irish Central, "The Foggy Dew" was written by Father Charles O'Neill and has been covered by several artists. It is about the 1916 Easter Rising and "encourages Irishmen to fight for the cause of Ireland, rather than for the British, as so many young men were doing in World War I."

McGregor later shared another tweet with a pair of photos, one with him posing with O'Connor and another with him raising his hands to her before the fight with an Irish flag draped around his shoulders.

The tweet read:

"The world has lost an artist with the voice of an Angel. 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 won the fight with a second-round TKO.

Here is a photo from that performance in 2015.

No cause of death for O'Connor has been given yet. However, London police did say the death is "not being treated as suspicious."

On Wednesday, O'Connor's family issued a statement confirming her death: "It is with great sadness that we announce the passing of our beloved Sinéad. Her family and friends are devastated and have requested privacy at this very difficult time."