ALLIANCES MAY CRUMBLE AFTER A TRIBAL BLINDSIDE, ON "SURVIVOR," WEDNESDAY, APRIL 29

"Friendly Fire" - Alliances may crumble after a tribal blindside, and an undercover operation escalates to new heights. Also, there's another brutal challenge on Edge of Extinction, on SURVIVOR: WINNERS AT WAR, Wednesday, April 29 (8:00-9:01 PM, ET/PT).

The following are the 20 returning winners competing in SURVIVOR: WINNERS AT WAR:

Ben Driebergen (36)
Winner of "Heroes vs. Healers vs. Hustlers" (2017)
Denise Stapley (48)
Winner of "Philippines" (2012)
Jeremy Collins (41)
Winner of "Second Chance" (2015)
Kim Spradlin-Wolfe (36)
Winner of "One World" (2012)
Michele Fitzgerald (29)
Winner of "Ka�h Rong" (2016)
Nick Wilson (28)
Winner of "David vs. Goliath" (2018)
Sarah Lacina (34)
Winner of "Game Changers" (2017)
Anthony "Tony" Vlachos (45)
Winner of "Cagayan" (2014)
Edge of Extinction: Natalie Anderson (33)
Winner of "San Juan del Sur" (2014)
Amber Mariano (40)
Winner of "All-Stars" (2004)
Danni Boatwright (43)
Winner of "Guatemala" (2005)
Ethan Zohn (45)
Winner of "Africa" (2001)
Rob Mariano (43)
Winner of "Redemption Island" (2011)
Parvati Shallow (36)
Winner of "Fans vs. Favorites" (2008)
Yul Kwon (44)
Winner of "Cook Islands" (2006)
Wendell Holland (35)
Winner of "Ghost Island" (2018)
Adam Klein (28)
Winner of "Millennials vs. Gen-X" (2016)
Tyson Apostol (39)
- Voted to Edge of Extinction for the Second Time Winner of "Blood vs. Water" (2013)
Sophie Georgina Clarke (29)
Winner of "South Pacific" (2011)
Left Edge of Extinction: Sandra Diaz-Twine (44)
Winner of "Pearl Islands" (2003)
& "Heroes vs. Villains" (2010)

SURVIVOR is hosted by Emmy Award-winning host Jeff Probst and produced by S.E.G. Holdco., LLC. Mark Burnett, Jeff Probst and Matt Van Wagenen are executive producers.

The 40th installment of the groundbreaking series coincides with its 20-year anniversary. For more information on the previous seasons of SURVIVOR, please log on to www.cbs.com/survivor.