As the series progressed, Montag began dating fellow cast member Spencer Pratt, which ultimately ended her friendship with Conrad.
She commented that she almost died from too much Demerol, reducing her heart rate to five beats per minute.
Later that year, they launched the Speidi Show, which was initially assumed to be a web series in which the couple used a different reality television format for each installment.
However, the project was later revealed to be an example of networked improv narrative, where Montag and Pratt collaborated with Mark Marino and Rob Wittig to create a Twitter game in which players Live Tweet an imaginary show.
In December 2013, Montag stated that she and Conrad have "talked a few times" since the series' conclusion, elaborating that "it's unfortunate things happened the way that it did, but we're both different people now, older and more mature." However, in 2015, Montag angrily excoriated Conrad when she appeared on Marriage Boot Camp, during a sequence where the contestants were asked to forgive someone who had hurt them in the past; Montag told a stand-in for Conrad that Conrad had "ruined my life with her lies", said that Conrad DID have a sex tape and had falsely blamed it on her, and that she "forgave" Conrad for being terrible and trying to ruin her life.
In 2006, Montag came to prominence after being cast in the MTV reality television series The Hills, which chronicled the personal and professional lives of Conrad, Montag, and friends Audrina Patridge and Whitney Port.
During its production, she briefly attended the Fashion Institute of Design & Merchandising and was employed by event planning company Bolthouse Productions.The couple, collectively nicknamed "Speidi", married in April 2009. In January 2010, Montag released her debut studio album Superficial; it was critically panned and commercially unsuccessful, failing to earn back the money she spent making it.Later that year, they made controversial appearances on the second season of the American version of I'm a Celebrity... She also received widespread criticism after undergoing ten cosmetic surgery procedures in one day.Montag was universally lambasted for bringing up the sex tape lies anew, parroting the views of Pratt (who Conrad actually blamed for spreading the false rumors; Conrad felt Montag knew he was lying but took Pratt's side because she loved him) and trying to use Conrad's name to get publicity for herself.She and Pratt appeared in the television special After Shock: Heidi & Spencer, which premiered on December 9, 2013, on E!, during which they admitted that many of the situations they were involved with in the various reality series they starred on were in fact made up by the shows producers.