Pop quiz: What does Korean pop star Psy and English singer-songwriter Ed Sheeran's grandfather have in common?
Answer: They both had a hand in Sheeran's newest album, x, which has just become the fastest-selling British album of the year.
Afire Love, the third of seven singles from the album, is "about my grandfather", the 23-year-old Brit Award winner tells Life! in a telephone interview from Los Angeles, where he is on tour.
He says he started writing it a few weeks before his grandfather, who suffered from Alzheimer's disease, died late last year. He completed the lyrics after the funeral.
He sings through the pain: "And things were all good yesterday/ Then the devil took your breath away/And now we're left here in the pain/Black suit, black tie standin' in the rain/And now my family is one again."
It is not all doom and gloom in the album, though.
The single Sing, released in April, two months before the full album went public, was inspired by a night out.
More interesting is the music video that accompanies the song - that was inspired by the time he went out for a night of karaoke with the Gangnam Style star.
The pair first met when they both attended the Billboard Music Awards in Las Vegas last year and have been in contact since.
Psy does not appear in the video but it does feature a wild, puppet version of Sheeran partying at karaoke and strip clubs and eventually getting arrested by the police.
"Oh yeah, I got to keep the puppet," Sheeran, a man of few words, says when asked about the video.
The album title, pronounced as "multiply" and not the letter x, was inspired by how he "was trying to multiply the size of the songs and the size of the production".
He adds: "It was a three-year process and I just wrote as many songs as possible."
He wrote 120 songs but ended up choosing only 12 for the album, which was released on June 23. He says: "I just made sure I listened to them as many times as possible and deleted the s**t ones."
His decisions have proven to be right on the money. Last weekend, the album sold 182,000 copies, beating the previous bestseller, Coldplay's Ghost Stories, by 14,000.
British music critics have given it mixed reviews though.
The Telegraph gave it a perfect score, praising Sheeran's "effortless absorption of contemporary musical styles". The Observer gave it only two out of five stars, saying that the songs "don't actually find a new gear for the love song, just new turns of phrase".
The singer reveals that he has plans to add Singapore to the Asian leg of his tour next year.
He says: "I think I'm coming early next year, yeah, we're hitting most of Asia."
Sheeran, whose parents ran an art consultancy, was born in what he described in a tweet as a "little English countryside" in West Yorkshire. He started singing at the age of four in the local church choir.
A keen songwriter, he released his debut EP, The Orange Room EP, in 2005 and started playing in small venues in London in 2008.
He had his first major break in the United States in 2010 when he was spotted by Oscar and Grammy winner Jamie Foxx, who was so impressed by his performance at an open mic night in Los Angeles that he offered the British singer his recording studio and let him stay at his Hollywood home.
Sheeran's fanbase started growing, thanks to several EP releases and the popularity of his songs on YouTube. One of the EPs, No. 5 Collaborations Project (2011), went to No. 2 on iTunes despite being an independent release with no music label doing the promotions.
The same year, he signed on to major label Atlantic Records, which released his debut album, +. It went straight to No. 1 in the British charts, while four of the singles hit the Top 10 in the country.
In 2012, he cemented his reputation as one of the UK's brightest young stars by winning two prizes at the Brit Awards - for Best British Male Solo Artist and British Breakthrough Of The Year.
The A Team, from his + album, also won Best Song Musically and Lyrically at the Ivor Novello Awards, one of the highest honours for English artists, and was also nominated for Song Of The Year at last year's Grammy Awards.
At this year's Grammys, he was nominated in the Best New Artist category but lost out to hip-hop duo Macklemore & Ryan Lewis.
Of his rise in the music industry, the bachelor says simply: "The last four years have been good and educational, my dreams have come true. I've toured the world and I've had a lot of fun."
Sheeran also has plenty of superstar friends and collaborators, including pop stars Taylor Swift and Harry Styles from One Direction, both of whom have inspired tattoos on his arm.
Sheeran and Swift became close when the latter took him as the opening act for her massively successful Red tour in the United States last year, an occasion which he marked with a tattoo of the Red logo. He also appears as a guest singer on a track on Swift's Red, the album the tour was named after.
They have not been working together recently but he does not rule out going on the road with her again.
He says: "She's been doing her album. I have been doing mine but yeah, I am not closing the door on that one."
x is out in stores.