The Bundesliga club said in February that they were parting ways with Tuchel. Nagelsmann, whose sacking in March 2023 led to Tuchel's arrival, was tipped to return to Bayern, but has now extended his contract with Germany until 2026.
"I have an agreement with the club, and it's communicated, and it stands," Tuchel told a press conference.
"I thought that this was going to be plausible after (director of the national team) Rudi Voeller renewed his contract and I think that Rudi and Julian really are a good team and work well together and support each other well, so I was expecting it.
"I believe for the national team this decision is good because it has clarity and stability ahead of the Euros without any discussions."
Bayern, league champions for the last 11 seasons, have already lost their Bundesliga title to Bayer Leverkusen this campaign, but they did reach the Champions League semi-finals after their 1-0 win over Arsenal on Wednesday.
That gave Tuchel's side a 3-2 aggregate win, and a rare moment of joy for Bayern this season, where they were also knocked out of the German Cup by third-tier club Saarbruecken.
"The atmosphere in the changing room was relaxed," Tuchel said.
"It's nice when the joy is so great. I sat down afterwards to relax with the coaches and friends. Waking up you're in good spirits, even if it was a short night, because we had training again the next day."
Bayern are at Union Berlin on Saturday, but will likely be without Leroy Sane. The winger missed the last two league games with injury and returned for the Arsenal win.
Sane may be rested to be ready for the following league match with Eintracht Frankfurt or the Champions League semi-final with Real Madrid.
"It will be a race against time for Frankfurt and Real," Tuchel said. "We probably won't take him to Berlin. It's unlikely."
Bayern are second in the Bundesliga standings, 16 points behind champions Leverkusen and ahead of VfB Stuttgart on goal difference.
