So close that Sam C even planted a kiss on Sam B at her album launch party!
Well, a kiss on her poster, anyway!
Cheeky popstar Sam C was among the celebrities who supported Sam B's big night on Thursday (4 August), and couldn't resist planting a kiss on a huge poster of Sam B while walking the red carpet.
On the tenth series of X Factor, Sam C was in the Boys Category mentored by Louis Walsh, while Sam B was in Sharon Osbourne's Over 25s Group. Sam B went on to win the show.
Mother-of-three Sam B, 39, landed the Christmas number one in 2013 with her cover of Demi Lovato's 'Skyscraper', supported Beyonce on tour, and achieved a number one album with her debut record The Power of Love.
She then left Simon Cowell's Syco Music label, flying to the US to work on second album Sing My Heart Out.
The first single from the album, 'Sing My Heart Out', is available now on iTunes. It was co-written by A1 star and singer-songwriter Ben Adams, who was also at the big launch. He's worked on numerous tracks on the album.
Sam B recently told her local paper, Leicester Mercury, that the song is dedicated to husband Craig and their children Brooke, Tommy and Miley.
Sam B's also announced a UK tour in support of the album, kicking off in March 2017 and going through until May 2017. Full dates and ticket details are available here on her official website.
And clearly Sam C is impressed by Sam B's new music, as he tweeted after the event: "Had a wicked night at my X Factor Mumma Sam Bailey's single launch!!! #KilledIt."