Alternate timeline (Father's Day)

In an alternate timeline, Peter Tyler never died in a car crash. Instead, his daughter, Rose Tyler, used the Ninth Doctor's TARDIS to save back in time and save his life. (TV: Father's Day)

Witnessing the event
Initially, Rose asked the Doctor to take her back to the day Pete died so she could be there with him, given no one was until the ambulance arrived, by which time he had already died. The Ninth Doctor agreed. The pair witnessed as Pete exited his car and was run over by a young driver, who quickly sped away in panic. However, Rose was distraught at witnessing the event, running away, unable to will herself to be with him. She confessed her regret to the Ninth Doctor, desiring to try again. (TV: Father's Day)

Interferring
Reluctantly, the Doctor took her back one more. They waited out of sight from their past selves, who were still witnessing the event. The Doctor informed Rose they could not risk another return and must wait for their past selves to run off before Rose could intervene. However, Rose impulsively ran out, in front of her past self and saved her father's life, pushing him out of the way. The effect of such a change caused the Doctor and Rose's past selves to disappear.

Rose and the Doctor then accompanied Pete into his house. Once alone, the Doctor chided Rose for her actions, remarknig her change to time would causecatastophic results. He eventually left, claiming he was leaving her there. Angered, Rose dismissed his threat and spent the day with her father, getting ready for the wedding he was meant to go to had he not died.

They arrived at the wedding, where the guests present revealed they had lost contact with others meant to come. People around the world mysteriously began to vanish also. In a park, a young Mickey Smith fled after the only children disappeared also. Rose and others also found their phones would only repepat the say message over and over when they tried to ring people.

The Doctor, upon returning to his TARDIS, found the interior had been taken out of time. Realising what was occuring, he raced to the church. Rose also met her mother, Jackie Tyler, and her younger self, discovering her parent's marriage was not as idyllic as her mother made her to beleive. The Doctor arrived shortly after, saving Rose from a Reaper. The guests fled into the church, as its age acted as a shield against the reapers. However, it wouldn't last as the Reapers gained more power as they consumed more people. The Doctor personally guessed the only survivors on Earth were people in similar old buildings like them.

Over time, the Doctor revealed to Rose saving her father had enabled the Reapers to infest reality, where they would cleanse it of everything to fill in the void made by her saving Pete. However, he refused to let Pete die again, attempting to save everyone by using his TARDIS key to pull the TARDIS back into their timeline. However Rose accidentally touched her younger self, enabling a Reaper to enter the church. The Doctor then sacrificed himself and his TARDIS to destroy the Reaper, there last hope lost. The Reapers eventually consumed the whole world.

Negation
Later, Pete noticed the car from earlier that day was stuck in a loop, driving round the church only to vanish. He figured out that the only way to restore the timeline was to allow the car to run him over. He tole Rose, having understood the Doctor had figured it out also, but tried to find another solution to spare Rose losing her father again. After saying goodbye to Rose and Jackie, Pete ran out into the road, avoiding the Reapers and allowed the car to kill him.

As such, a new timeline was created. This time, Rose was by her father as he died and the runaway driver stayed instead, allowing everyone to know who he was. (TV: Father's Day)

Rose later told Jackie she was at her father's side as he died, rather that not so as originally occurred, in an effort to prove to her mother how wonderful the Doctor was. (TV: The Parting of the Ways)