Question: Who was the featured singer in Katy Perry's song "E.T."?

Context articles: Purr by Katy Perry
Katy Perry
Katy Perry: Part of Me
La Coacha
E.T. (song)
MTV Unplugged (Katy Perry album)
Ammo (musician)
Katy Perry Live: Witness World Wide
Katy Perry discography
Ester Dean

Purr by Katy Perry is a fragrance created by American singer Katy Perry and Gigantic Parfums.
 Katy's love for cats and kittens influenced both her decision to create the perfume and its design, although further inspiration for the bottle's design came from other perfume products worldwide.
 Purr features a variety of scents, including citrus fruits.
 Released in November 2010, it is available in a purple cat-shaped bottle.
 Purr is available in 1.7 and 3.4 fluid ounce bottles, with a retail price in the US of $35.00 to $45.00 for the smaller size and $65.00 for the larger.
Katheryn Elizabeth Hudson (born October 25, 1984), known professionally as Katy Perry, is an American singer and songwriter.
 After singing in church during her childhood, she pursued a career in gospel music as a teenager.
 Perry signed with Red Hill Records and released her debut studio album "Katy Hudson" under her birth name in 2001, which was commercially unsuccessful.
 She moved to Los Angeles the following year to venture into secular music after Red Hill ceased operations and she subsequently began working with producers Glen Ballard, Dr. Luke, and Max Martin.
 After adopting the stage name Katy Perry and being dropped by The Island Def Jam Music Group and Columbia Records, she signed a recording contract with Capitol Records in April 2007.
Katy Perry: Part of Me (advertised as Katy Perry: Part of Me 3D) is a 2012 3D autobiographical documentary film on Katy Perry.
 It was directed by Dan Cutforth and Jane Lipsitz and released in the United States, Canada, the UK, and Ireland on July 5, 2012.
La Coacha is a Mexican-American comedian, singer, blogger and internet personality.
 She became Perez Hilton's protégé after 'stalking' him for a number of years.
 Her videos are often featured on his website.
 La Coacha's internet videos are popular, with her parody of Lady Gaga's Alejandro totaling over three million views.
 Her parody of Katy Perry's "California Gurls" titled "Kardashian Gurls", was her first parody available for purchase on iTunes.
 Perez Hilton raps in both the song and the video.
 Kim Kardashian, Khloé Kardashian and Katy Perry all admitted to loving the video.
"E.T." is a song by American singer Katy Perry from her third studio album, "Teenage Dream" (2010).
 She co-wrote the song with its producers Dr. Luke, Max Martin, and Ammo.
 "E.T." was serviced to radio stations as the album's fourth single on February 16, 2011.
 One version of the song features verses from American rapper Kanye West.
 Musically, it is an electronic and hip hop ballad which draws heavily from dubstep and techno, along with smaller amounts of drum and bass.
 According to Perry, the song lyrically speaks of "falling in love with a foreigner".
MTV Unplugged (listed on iTunes as MTV Unplugged: Katy Perry) is an extended play (EP) and live album by American singer Katy Perry, released in the United States on November 13, 2009 by Capitol Records.
 After airing more than 100 "MTV Unplugged" specials, MTV wanted to bring back the series, in order to expose them to a younger generation.
 The channel recruited various mainstream and popular artists to perform as part of the series, including Perry, who particularly expressed interest in the idea as it would allow her to showcase herself as an artist and share the stories behind her songs.
Ammo (born Joshua Coleman) is an American record producer and songwriter.
 Ammo has co-written and produced songs for Beyoncé, Kesha, Katy Perry, Pitbull, Maroon 5, Britney Spears, Jessie J, Jason Derulo, Mike Posner, Fifth Harmony, R. Kelly, Flo Rida, and Selena Gomez.
 Ammo has contributed to hits such as Maroon 5's "Sugar", Katy Perry's "E.T.", and Fifth Harmony's "Work from Home".
Katy Perry Live: Witness World Wide was a four-day YouTube live stream by singer Katy Perry airing between June 8–12, 2017.
 The special features Perry living in a "Big Brother"-style house with cameras promoting her fifth studio album, "Witness".
 It began on June 8, and concluded with a free concert on June 12 in Los Angeles.
American singer Katy Perry has released five studio albums, one live album, two extended plays (EP), 27 singles (including three as featured artist), and five promotional singles. Perry has been certified for 90 million digital singles and 6 million albums in the United States as of August 2017.
 She is also the third best selling digital singles artist in the US according to Recording Industry Association of America (RIAA).
 As of November 2012, Perry has sold over 100 million records globally.
 She currently holds the record for most 5-million-selling singles in the United States, with six of her singles selling over 5 million (in order of release date: "Hot n Cold", "California Gurls", "Firework", "E.T.", "Roar", and "Dark Horse").
 Perry also holds the record for the most 6-million-selling songs, with three of her songs—"Firework", "Roar", and "Dark Horse"—selling over 6 million copies.
 All three have also received Diamond song certifications from the RIAA, making her the first artist to accomplish such a feat.
Esther Renay Dean (born April 15, 1982), known professionally as Ester Dean, is an American singer, songwriter, record producer, and actress.
 Her 2009 single "Drop It Low" featured singer Chris Brown.
 Dean has also co-written songs for many artists including Christina Aguilera, Florence + The Machine, Katy Perry, Beyoncé, Nicole Scherzinger, Priyanka Chopra, Mary J. Blige, Nicki Minaj, Kelly Clarkson, Ciara, The Pussycat Dolls, Usher, Kelly Rowland, Girlicious, Keri Hilson, Rihanna, R. Kelly, Britney Spears, Melody Thornton, Vanessa White, Kevin McHale, Selena Gomez, G.R.L., Soulja Boy Tell 'Em, Little Mix, Pia Toscano, Tinie Tempah, Lil Wayne, Machine Gun Kelly, Fifth Harmony, and Eurovision Song Contest 2012 winner Loreen.