David Tennant's final lines as the Tenth Doctor both times were, "I don't want to go." He said them right before his regeneration, and before entering his TARDIS in "Day of the Doctor" in response to his reckoning on Trenzalore. However, he didn't say them as the Fourteenth Doctor at the end of "The Giggle," the last Doctor Who 60th Anniversary special, because he didn't actually go anywhere. Instead, he bigenerated with Ncuti Gatwa's Fifteenth Doctor. Interestingly, thanks to bigeneration, Russell T Davies created the perfect solution to Billie Piper's problem with the way her character Rose Tyler's story ended. In this case, she was locked away in a parallel universe with a human copy of the Tenth Doctor.
Source：https://www.cbr.com/doctor-who-bigeneration-tenth-doctor-rose-tyler/
