How I Met Your Mother Season 4 Episode 15 (03/02/09)
When Barney passes on hitting on some floosies at the bar, the gang begins to notice that Barney has been acting differently. Plus when Marshall recalls Barney saying I love you to some woman on the phone, they begin to suspect he's dating someone and they follow him as he leaves the bar. When they arrive at the house, we meet Barney's mom, Loretta (Frances Conroy).
Soon after, the gang meets Barney's wife (Brooke D'Orsay) and son (Angelo Diona), which they soon discover have been hired by Barney as part of an elaborate scheme to make his mother happy. It turns out when Barney's mom was sick, all she wanted was for her sons not to be alone like her so he lied and said he had a wife. When she then said all she wanted was a grandchild, his fake wife said she was pregnant and soon he had to hire a fake kid. Barney has managed to keep up the lie to his mother for years.
When Ted manages to bond with Barney's fake wife over some play he saw her in, the two soon end up making out in the kitchen and everyone walks in on them. Barney eventually comes clean about the lie to his mother and she admits she never liked his fake wife or kid.
Meanwhile, Lily admits to Marshall that she never like his mother. Marshall is devastated throughout the epiosde and at the end Lily fakes a phone call to his mother to apologize for being so cold. On the other end is actually Ted and Barney's fake wife. Poor Marshall is filled with tears of joy and doesn't find out.