Thibaut Courtois left Chelsea on bad terms last summer and he expects to feel the anger from Atletico Madrid too when he faces them in the white of Real Madrid on Saturday.
Courtois developed into one of the world's finest goalkeepers during three years on loan at Atletico but he will be up against his former club, and Chelsea team-mate Alvaro Morata, in what could prove a pivotal city derby this weekend.
Real arrive on the back of four La Liga wins on the bounce and will jump above their opponents with a win at the Wanda Metropolitano. Atletico have fallen six points adrift of Barcelona and are attempting to stay in touch.
For Courtois, a reunion with Diego Simeone's side is not new -- he faced them twice for Chelsea in the Champions League last season and again at the Santiago Bernabeu in September -- but this will be his first experience in front of the Atletico fans, in the colours of Real Madrid.
"It happens in football, it's a derby and a derby here in Madrid is always heated," Courtois said.
"They'll whistle and shout, everything you would expect, it's part of football. I will always respect them. Now I'm playing for the other side."
Courtois helped Atletico crack the duopoloy of Barca and Real by winning La Liga in 2014, while also lifting the Europa League, Copa del Rey and Super Cup during his time at the club.
"There are still a lot of players that I know there, the goalkeeping coach, coaches, they're all still the same," Courtois said.
"It's still a special match, I respect the fans and the club a lot, in the end they gave me the opportunity to play when I was just 19 years old. I only have good memories."
Courtois' season has taken a similar trajectory to his team's. There was a shaky start, when Julen Lopetegui rotated him with Keylor Navas, before a clear improvement, with Courtois now established as Santiago Solari's first choice.
Madrid have steadily gained momentum under Solari too and, despite a dip at the start of the year, have found their rhythm in recent weeks.
"I feel good now. It takes a little time to settle and to fully understand the team but it's going very well now," Courtois said.
"If we want to narrow the gap and win trophies, this is the month when we have to be at our best."
Like Courtois, Morata pushed hard for a return to Spain and was granted his wish last month, after his form had plummetted at Chelsea. Eden Hazard could be next, with the 28-year-old expected to follow Courtois to Real in the summer.
"Eden is a great player, one of the best players in the world," Courtois said. "He is a great friend of mine and if he comes here I would be very happy but at Chelsea, he's a god there too."
After eight league wins in a row, Barcelona have now drawn against Valencia and Real Madrid in the Copa del Rey.
They face a tricky trip to Athletic Bilbao on Sunday but Ernesto Valverde was hopeful on Wednesday that Lionel Messi would be fit to play at San Mames.
Messi came off the bench in the second half against Real but the Argentinian could return, along with Ousmane Dembele, who has recovered from an ankle injury.